Fellow developer likes to request changes on pull requests to do major refactors on untouched code or change functionality which is outside the scope of the ticket.
Manager doesn't work on the codebase and doesn't care. This blocks our work and we often have to submit to their demands.
Feels very micromanagy even tho we are all experienced.
Asking for advice and a friend. (mostly a friend)

What does the manager have to do with any of it?

Pair on your next ticket with them and ask them about it OP.
Thats what we've done and its paid off handsomely.

Review each others code often and build a good working relationship as well as an understanding of why each of you have these differences in what you both think does or doesn't needs refactoring.

They might have a good reason for it or they might not. You won't know until you both try it out together in real life against real deadlines.

Discuss things like: pragmatically picking which battles to fight, and focusing refactoring on areas of the code where it'll actually pay off and help your team improve in development efficiency. That code might never be touched vs high churn areas that are awful to develop in.
"Biggest bang for your buck" sort of idea.

Remember that is no industry "right" answer to how much to refactor, otherwise our industry would be less of an art and more of a science.
Refactoring needs doing but it needs doing well which includes doing it efficiently

@MammaNeedHummus thank you. The recent problem has been with this person is that when we've already gone through the steps, then they ask have you tried xyz. And we explain we have and even then they make it look like it's always been their idea.
They always get worked up when we explain our thought process. Unsure. May be an anomaly

@mucalena oh that doesn't sound nice sorry to hear