I use “floating dock” extension (it’s a “better” fork of dash 2 dock) and I kept getting double docks (i.e. the floating dock ontop of the standard one) so I removed it :
sudo apt remove gnome-shell-extension-ubuntu-dock
and that got rid of the double dock issue… I don’t know if “floating dock” works in Gnome 4.x or not… Sorry…
It think the lack of “dash 2 dock” extension in Gnome 4.x was what convinced me not to use Fedora 34 when I recently tried it out… I kept jumping / hopping till I ended up back at Ubunu 20.04 again…
I probably won’t go any further (i.e. 21.04, 21.10 or 22.04) until I’ve seen fixes / updates for a few things :
- dash 2 dock extension working on Gnome 4.x
- method to disable the UGLY Microsoftish forced update on boot
Seriously? - a Linux system, after booting past grub, “Updating, do not turn off your computer…” Well, I have no idea how long it would have taken because I DID TURN OFF the computer and went distro hopping 
…
I’ve tried a few google-fu hunts for “how to prevent Ubuntu 21.04 auto update” but ALL I GET ARE FREAKING dummies guides about how to update to 21.04 or 21.10!!!