MV3 itself isn't what breaks uBlock Origin, it is the bundled removal of capabilities that Chrome decided to do. Firefox MV3 supports full WebRequest "scopes" while Chrome only supports declarativeNetRequest.
I know Chrome has some additional limitations, and in a vacuum MV3 doesn't break UBO as hard - but is blocking of the "Element picker" part of that or inherent to MV3? I rely on that a lot.
