I'm gonna say you are in the minority there. Firstly, a Review should be just that a review of the code - not just a blind acceptance of a button. Its going to be hard to properly review code, which may be across multiple files, or may require switching within the same file, on a phone.
And secondly, work life balance, just because you can work while waiting in line for groceries doesn't mean you should
Firstly, I know my repo quite well and can generally (not always) tell whats happening with a PR without having to switch too many files. Even if I need to do that, I've been able to do that just fine on GitHubs desktop page so if it's not easy on a mobile now it's just a usability problem. It's a little bit much to say there's only one right way to do PRs or even write code.
Secondly, work life balance is a choice. Glad you make it, no one should ever be coerced against it, but I want to choose what I do. I'd rather look at my company code than what Kim Kardashians butt looks like on the Us weekly issue in the aisle. Also a bit presumptuous to assume it's only work, I have a personal website as well and I actually want to work on that whenever I have downtime.
My main usage of the app so far has been to approve PRs when pair/mob programming. Instead of going back to my desk where my computer is, I can approve the PR I've co-authored immediately.
Obviously it's quite a narrow use case, but I imagine there are lots of similar cases where the review is simple for one reason or the other and you want to get it done quickly.
Why would you need Codespaces for that? They released a standalone GitHub app recently just for this purpose. Not sure if it also works with the web version. But Codespaces seems to be the wrong tool for this job.
Their app is still outrageously feature incomplete in some ways. Can't create a branch! Can't edit files! Still better than their mobile site though but I end up opening their site in desktop mode to do any real work on my mobile. Super annoying!
And secondly, work life balance, just because you can work while waiting in line for groceries doesn't mean you should