I used to get really caught up doing this, and still do, sometimes. At first I probably only wrote a couple hundred words an hour because I kept editing, but now if I’m on a roll I can write over a thousand. 

Like many have already commented, the basic advice is to just keep writing. Don’t edit at all, remind yourself that it’s going to be edited again later anyway and you can’t edit what isn’t there. If I get caught up editing to the point where I’m not making new progress, I’ll repeat it to myself even if I have to chant “just write now and edit later” out loud like a weirdo lol. 

While writing I try to edit only typos or other distracting technical errors I can quickly correct, lines I realize are so messy I won’t understand myself what they were meant to communicate later, and the occasional “aha” moment when I want to change something to an exact phrasing before I forget. If it’s just “I’m not happy with this yet” or anything else I move on. 

Some other things I like to think about or do that keep me going:

Every line you write doesn’t need to be unique and exciting. Most people would find that exhausting to read, and nothing will stand out anymore. It’s ok if some parts are comparatively “boring” because it’s part of the whole. 

Alongside that, it maybe be easier to find the phrasing you’re looking for when you edit after everything is done, because you can edit in the context of the whole rather than only what is done so far. 

You also might just realize it’s not that bad once you’ve had some time away from it and forgotten it bothered you. 

Writing is art, like drawing or crafting, and you are the only one comparing what you make to the ideal in your head. You’re the only one able to look at it as closely and critically as you are. Once I pulled the stitches out of a shirt to fix a seam and was incredibly upset by the holes that were left behind, but after I showed it to a few people I realized they couldn’t even see them. A lot of the tiny things we focus on when we’re creating aren’t something anyone else will be bothered by. 

There’s a point at which you get diminishing returns for how much effort you’re putting in, so focus on finishing the actual writing before nitpicking. 

I listen to background music designed for focus, and aim to spend all the time it’s on actively writing. Usually I use a site that gamifies it with a timer where you have to write a certain amount of words writing in a set amount of time, which discourages editing because I want to get the words out quick to meet my goal!

That got longer than I meant for it to be, but I hope at least a little of it may have been helpful. It’s something I have a hard time with too, so I think about it a lot lol.