What you describe is not possible with Github at the moment. With Push rulesets, you could at least block changes to certain files entirely. Unfortunately, this does not integrate into the PR workflow because the git push operation is blocked.

https://docs.github.com/en/repositories/configuring-branches-and-merges-in-your-repository/managing-rulesets/about-rulesets

With push rulesets, you can block pushes to a private or internal repository and that repository's entire fork network based on file extensions, file path lengths, file and folder paths, and file sizes.

We use this feature to prevent changes for certain test files. If a rare change is required, some (senior) developers can bypass this rule.