It all comes back to figuring out what is making you feel bottled up once you’ve written up to a certain point. Could be you just need a break, you’re feeling like certain parts of the story aren’t as fun, you’re getting bored, burnt-out, etc. If you can fish around for the answer to why you’re losing motivation (no judging yourself; nothing wrong with having writer’s block), it’ll be easier to know where to go from there.
Here’s a few different articles I’ve found helpful (or at least interesting) at some point or other:
https://susandennard.com/2013/10/21/how-i-plan-a-book-part-4-coaxing-out-the-magical-cookies/