Hello, I gave it a try over the week end, with a clean install. The first part, creating the Catalina USB, and installing Catalina went smooth.
Problems started when rebooting trough the USB key but on the main HD in order to install all the necessary kexts with MultiBeast. For the first time ever I had a failure to install from MultiBeast. I then installed the kexts by hand.
From this point I fell in the nightmare loop of a known issue but that I was unable to solve. It's the one where the boot get's stuck at " IOConsoleUsers: gIO ScreenLockState 3 ", for example on this
thread
From them one I tried the different proposition of fix found on the site, but without success as for now.