Yes, people (myself included) often use tab for easily navigating pages for either convenience or accessibility reasons. For example, if you’re in a form with a lot of inputs, often instead of moving your mouse over to the next box you can press tab and it’ll go to the next one.
Hello, I am using desktop (Windows 11 24H2). I saw earlier posts showing that the theme select works so I don’t know why this occurs over here. I can download Firefox and test that, however.
You can try using your phone and making sure Discourse is fully up to date (the theme is always tested against latest tests-passed commit), otherwise I’m not sure what your issue could be, sorry!