For what it's worth (excluding client-side issues), I have a high-speed internet connection and a last-gen CPU.

Things that are very slow (from 5 to 60 seconds depending on the number of items) for me:

- Clicking on "Pull requests" tab for any repo

- Opening a PR with many comments (50+)

- Opening "Files changed" tab from inside any PR

- Marking a file as "viewed" from the "Files changed" tab

Tips I found to mitigate this:

- Opening the link in a new tab often usually only takes half the time than navigating in your current page.

- Review PRs from the visual studio code web ui (github.dev), easily accessible by pressing "." while viewing a PR