I've been coding for over a decade including things 1000x as complicated as that (think embedded systems from the ground up). I could easily take 20 minutes or even fail doing such a task because I'm literally never asked to code things in a professional environment with 3+ strangers breathing down my neck and judging me based on some simplified fizzbuzz.

I'm convinced white board / live coding interviews don't do much other than test for how you perform with a group of strangers pressuring you to jump through hoops publicly on which in a short time your entire value is judged (including determining say if you'll have money for daycare next week), which for most software professionals basically happens never except during an interview.