It’s just awful. An accessibility disaster, and I don’t say such things lightly (normally I might just say it has serious problems).
If I come across much more usage of Notion, I’ll need to craft a user script to unbreak as much as I can. document.querySelectorAll('[contenteditable]').forEach(e => e.contentEditable = false) is a good start, fixing the focus issues. Unfortunately all their event handlers are on the root element, so you can’t just clobber them with document.body.outerHTML = document.body.outerHTML or similar but must figure out some other way of deregistering or breaking their event handlers.