[vanjajaja1]

Hard to say without more info about the relationships and company structure. It looks like this person is pushing back on your judgement with their own judgement. If you can't fall back to finding a mutual understanding then you're at battling for power. If you have the seniority you can just say "No, this is the standard that the team agreed on and we enforce, your PR is not being approved until it is fixed", and if you don't then I think you need to involve someone who is one level above you to resolve the judgement dispute.

If you're not willing or able to clash, you'll have to try find some compromises that improve the situation but make for an undesirable choice for this person. eg. In the PR example, require that large PRs require an in-person walk through.