Took awhile for me to notice, but trying to making changes to the Pane Groups is different now.  Left Clicking no longer drags one out to a separate pane as it used to. Looking for some more info, the latest avail on YT is The WP Guru and is using 4.21, and that's key thing he's doing.

Tried Alt drag, etc. and no go. In fact, you no longer get the double-direction arrow when over the divider line.

Right clicking menu doesn't help much, nor does having TWO options for the Documentation help. Seems to me having an Editor with an arrow, but that only gives you the Documentation option is a mistake or incomplete.

Anyone?