Downgrade after failed Catalina install? I am trying to upgrade an iMac to Catalina and the upgrade process keeps failing. macOS is not booting back into Mojave either.

I have already tried the following:


Disk utility first-aid
SMC reset
NVRAM reset


Is there a way to get back into Mojave or get the Catalina upgrade going again?
I couldn't find an answer to the issue. At the last stage of the installation process the installer informed that it couldn't remove the previous version of macOS and rebooted. 

After that, macOS enter in an infinite loop of kernel panic upon every boot. Gave up, erased the disk and installed from USB.

Perhaps the solution under Un-Assigned Kernel Misfiring on this link could have solved my issue, but I only found it after reinstalling macOS from scratch.