I clicked on “mark all as read” not knowing what it was. Can you add hover text for icons that aren’t textual? I’m thinking of the “mark all as read” icon as well as the home icon (pretty obvious) and the Interactions/Activity icon (not as obvious).
It should have a tooltip already. Have you turned off tooltips in Preferences?
I do (vaguely) remember turning that off. Now that it’s back on, the Mark All As Read icon doesn’t have a tooltip. Is there supposed to be one for that icon? I can try a few more things if so (already turned off extensions in Safari, restarted the browser).