I just encounter the issue of no more pop up under youtube. But it's odd cause I was pretty sure it was working during my current session.
My solution is awkward, I simply use one of my workspace that I have not recently modified. The issue only happens when I am in my 3rd (of 4) workspace (one that I modified recently, like the icon and the name).
More context : I installed 'opera one' on a new machine 2-3 weeks ago under win 11. I have synchronized my account to recover bookmarks, etc. As a side note, the synchronization process cleared the entire content from 2 of my workspaces on the original machine, which is always nice to have no warn when things are deleted/cleared/removed ... Would have been nice to have a way to recover my 100+ opened tabs :p

Resume : check if the popup issue is present in all of your workspaces.