Thought this problem was due to my older 2017 Intel MBP and OS 13.6.7, but sounds like this happens on newer systems too. Error occurrence is random, sometimes several times a day, sometimes only once every few weeks. Safari disallows input in the URL bar, scrolling locks, and I need to quit, restart, then reopen all tabs from history. It's regular enough to be a real productivity sink, but not an error I can reproduce on demand, so Support is no help here.
It's a shame - Safari has been my go-to browser for security, privacy, and (relative) simplicity. I'll need to move everything over to Firefox I guess.