installation from usb stick not possible (final), from beta it lasts about 30min (one try) until the installation process starts. On the forums there are many, that have the same problem.
20.03 works without problems. Is the solution to install 20.03, wait for the new upgrader, and upgrade to 21?
It looks like there is a problem with the isos, but i am not sure (as i am just a simple user)
cheers, Bernd