It sounds like someone's identified a social problem and tried to fix it purely with technology. I'm talking about code review. Knowing no more than what you've told us, I would guess you need some social changes too.

The problem is complex, but the first place I would consider starting: try supplying a break-glass "I want to merge this without review", but have a zero-tolerance policy for unreviewed breakages. If you break something, and it turns out you did so in an unreviewed PR that you just YOLO'ed in, you are buying cake (or whatever). People need to learn from experience that reviews really are great, and one way to show them this is by making it clear how bad it is when there are no reviews.

Note, too, that now you are working with branches, there are tons of probably-unrealised benefits available to you. Pre-merge automated test suites, for example. Personally, I would flatly refuse to work on any moderately-complex code base that did not have automated branch tests that ran before any merge to master. It would almost certainly be well worth some dev effort setting this up, because it genuinely is a huge benefit to the branching workflow.