At high levels in dnd and Pathfinder and similar games, combat takes literal hours to get through. If you only play for a few hours at a time, then there are some game sessions that you're not playing a roleplaying game, but a wargame. You may be roleplaying in the sense that you are using your character's moral alignment and martial skills to bring the battle to a favourable end, but that's the same level of roleplay as many wargamers use in their games. The problem for many players and game masters is how to keep roleplaying as the focus of high-level adventures, but still feel like you're progressing as a character in a system that mostly rewards you for combat. I've got 3 options, each of which I've tried with different groups (or the same group in different campaigns).
Before I present each technique, I have a few caveats. First of all, I'm presenting this game loop as a problem, even though sometimes it's not a bad thing. Some people (including me) appreciate an equal balance of roleplay sessions and basically-a-wargame sessions. I'm happy to spend a few game sessions exploring a dungeon and talking to NPCs and solving riddles, and then a whole evening on just one battle. It's not a problem for me, I just know as a game master that for some people it is.
Secondly, all of my techniques to mitigate the problem [assuming it's a problem] require you to "sell" something to your players. These techniques go above and beyond the default game modes that most people are familiar with, so you have to lay some groundwork early, and "train" your players to accept some new options as part of the game. It's not something you can just drop into a session suddenly one evening and expect it to be adopted, or to even make sense.
One easy way to avoid neverending combat is to avoid combat. You can do that in-world by just having the thugs and brigands and guards and even orc raiding parties or whatever just back down before the killing begins. You have to be a little careful when doing this, because it does initially feel weird to players to be awarded XP without drawing blood. It confuses the parameters. Is the new rule for earning XP that you just have to intimidate someone?
The way I do it is that I start initiative, while declaring that we're entering negotiations, and that no one has drawn their weapon (or charged, or whatever) yet. If the baddies have inititiative, they start talking, asking questions, or making some demand (but not a threat.) If the players have initiative, then I ask the player what they'd like to say to the baddies (as opposed to an open-ended prompt like "Your turn" or "What do you do?") If the players put forward a pretty intimidating or persuasive argument to de-escalate the situation, combat is successfully avoided and XP is awarded. It doesn't feel like a cheat, because players rolled for initiative, and had to wait their turn to talk. That's basically combat, and we all know that combat means XP.
This is a trick I adapted from Pathfinder's Ultimate Intrigue, and it works really well. In Pathfinder 2, initiative isn't even based on Dexterity, but on whatever skill is relevant to the situation, so for this kind of verbal combat, I tell players to roll initiative using their Charisma modifier. You can steal that for dnd, too: "Roll for initiative, but also add your Charisma modifier." It takes players by surprise the first time you do it, which can be good for broadcasting that something's different about this combat.
Sometimes the only reason players look for fights is because it's the only reliable way the game provides them for character progress. (That's not always true, of course, some people just enjoy combat, so take care when diagnosing this as a problem.) To get around that, all you have to do is demonstrate to your players that substantial XP can be earned outside combat. This technique works best when you let the players discover this on their own, I think, because otherwise it's just your word against the Player's Handbook or years of tabletop experience.
I always hand out XP for finding secret doors. I don't remember when or why I started doing that, but it just seemed natural to reward the players for it, after it started requiring a skill check to accomplish. I also reward players for doing nice things for NPCs, like leaving little notes in dungeons to warn future adventurers of danger ahead. I've rewarded XP for making smart decisions when navigating a new city ("you've successfully avoided a group of thugs who were lying in wait down that dark alley"), or for finding hidden treasure, or a significant book or collectible item, and so on. It's a lot of rewarding positive behaviour, where "positive" is defined as you seem to be having fun, so keep doing things you enjoy for more XP.
This sort of thing can come across as very arbitrary, because it is, and that can be frustrating to a goal-oriented player (like myself). I don't want to be surprised and delighted by arbitrary XP, I want to know how to earn XP, and then I want to go do that, For that reason, I often just state the XP reward for a quest up front. When the player characters are negotiating for gold pieces with the noble asking them to go recover the MacGuffin, I break from the conversation and, as the game master, tell the players how much XP the quest is worth. If the player characters talk the noble up in price, then the XP goes up a little as well. I avoid the 1:1 gold-to-XP ratio because I've learned that making XP a "tangible" item in-world leads to a whole series of tedious debates that I don't find particularly enjoyable ("I just sold a short sword for 5 gold crowns, why don't I get 5 XP for that?")
My point is, when you reward players XP for having fun, you demonstrate that players don't have to go looking for a fight. Coming up with your own list of things that players get XP for is, I think, a process in itself, and it can even be unique to each group, based on how they play. The important thing is to be consistent so it's as reliable as combat, and when you make a mistake, admit to it and offer to formally change the rule.
It can be useful to incorporate structured roleplay, and this works especially well in a low-fantasy setting. You can encourage roleplay during combat by including a roleplay phase into your combat sequence. It doesn't make combat go faster, but it can make it more fun.
The way I do it (when I do) is essentially enable an additional action type called Negotiation. It's unique from the free action of saying something out loud while you otherwise hack and slash at your enemy. Instead, it takes up an Action and usually (but not always) displaces the Attack action on your turn. Negotiation is essentially a verbal duel, again taking notes from Pathfinder's Ultimate Intrigue but also a heck of a lot from Ragadorn Ale-House Brawl. When you Negotiate with an enemy, there's a high probability that the enemy won't be able to attack you in response. As the game master, I try to take whatever Negotiation bait a player throws at my enemy, with the only exceptions being when the player is using the completely wrong tactic (but even then, it might force the enemy to ask "Hang on a moment, that's not why I thought we were fighting, what do you think is going on here?") or when the enemy is a big evil boss who exists only for this exact battle. Sometimes I'll have the enemy do a morale check (or Leadership, or Charisma, or Intelligence, of Cool, or whatever your system offers) to resist the Negotiation. But usually resisting the attempt to Negotiate is only to make a point to the player about motivation, because really the only reason Negotiation exists as a mechanic is to offer turns of not fighting.
Once a player character has entered Negotiation, I just keep the conversation short and to the point, and then move on to the next Initiative count. You might think that allowing back-and-forth conversation breaks initiative, and it kind of does, because responding to a Negotiation does happen out of turn. Unless you play with a highly efficient group, I find it takes the same amount of time for a focused back-and-forth conversation as it does the party rogue to finish a few backstabs and a dodge and hide and an extra move and a bonus action and, oh yeah I forgot, a bonus-bonus action, and oh yeah, I was supposed to be rolling with advantage the whole time so let's start over action.
That said, if you're at this option then you're in combat, and this post is meant to help you avoid combat. This is a technique I use, obviously, when combat happens either because some people in the group enjoy combat and other people don't, or because the other techniques have failed and the story just logically demands combat. It doesn't work against brainless monsters or against an embodiment of ultimate evil. In fact, you really have to avoid it in those cases, because it can really threaten the gravity of the situation. Letting the big bad villain even roll to consider listening to reason can really ruin the villain's persona.
Negotiation doesn't have to be literal negotiation, though. It can just be a discussion, like "why are you willing to die to protect this tomb?" rather than "will you walk away from this fight if I offer you this many gold pieces?" What it's not meant to be is banter or taunting. It's supposed to be a meaningful conversation, as an option to players who want to investigate a situation further even though their fellow players (or the game master, who knows the enemy's motivation already) have rushed into combat.
A lot of these techniques work best when you incorporate them into your game early, not as rules that players must adhere to, but as demonstrable options players have in the event that they discover they're not really excited about combat. I also use some of these options in wargames as a way to incorporate roleplay options into a battle. Finding the right balance is important, but that's true of most game master techniques, even when those techniques are written as official game mechanics in the rulebook. That's not a bad thing. It's why we play tabletop games with other actual humans. We can adapt and remain flexible based on what the group finds enjoyable, whether it's through level progression or just over the course of a single game session.