In codebases where PRs are squashed on merge, the commit messages on the main branch end up being the PR body description text, and that's actually reviewed so tends to be much better I find.
I've seen it be the concatenated individual git commit messages way too often. Just a full screen scroll of "my hands are writing letters" and "afkifrj". Still better than if we had those commits individually of course, but dear god.
The gold standard is rebased linear unsquashed history with literary commits, but I'll take merged and squashed PR commits with sensible commit messages without complaint.
And in every codebase I've been in charge of, each PR has one or more issue # linked which describe every possible antagonizing detail behind that work.
I understand this isn't inline with traditional git scm, but it's a very powerful workflow if you are OK with some hybridization.