Downgrade after failed Catalina install?
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.