You should pull the PR you're reviewing down into your IDE and you should spend like, an hour reviewing it carefully and trying to break it. Have a mental checklist: say they renamed a function ... is the file named the same as the function? Did they remember to rename the file? Did they delete parts of the code? Did they remember to delete everything related to that? Often the most challenging parts are negative: it's harder to remove properly than it is to add new things. Say they changed the validation on a model: is this going to work well with the production database? Do we need to write a migration to catch the database up to the new reality of the code? Automated tests are just automated warning flags that give you confidence that the codebase is basically hanging together. You still need to be very careful & thoughtful as you're making changes.

I like to actually reset the branch so I can see all the raw changes in my IDE, this helps me to think it through, in git you can do this via:

git pull feature-branch; git checkout develop; git checkout -b my_initials/feature-branch; git merge feature-branch --squash --no-commit