Reviewing PRs on GitHub is embarrassingly bad, given that it's their core feature. It hasn't been upgraded for years, even, missing features BitBucket/Stash had like 10 years ago. Now a file tree is finally in beta, so it's possible to navigate between the files. But it's still impossible to see the context around changes without having to press expand/(...) a hundred times.

I've recently experimented with the PR feature inside JetBrains IDE's. It allows one to navigate quite well without having to actually switch branch. Like it so far, nice to see the whole file and related files, not just the diff.