Just stumbled across this thread and thought I'd share my findings so far. When complete, your Mac will start up as usual. The reinstallation process will start shortly and roughly take 30 minutes. Select the hard drive you’d like to reinstall mac OS Catalina to and click Install In the first window, select Reinstall macOS ➙ Continue Restart your Mac and then hold down ⌘ + R to activate Recovery Mode The correct way to reinstall macOS Catalina is to use your Mac’s Recovery Mode: While not a totally fresh install (old apps could still gum up things) It is possible to reinstall the os from Catalina recovery mode:

I think it just needs to start out on a clean fresh drive but I can only relate my experience.

I did a 4K Final Cut Pro x project and Catalina preformed better then it ever has (I’ve used FC since version two). I feel Catalina is a very different OS then past ones and some apps aren’t compatible so I didn’t do an update but a 100% clean install of Catalina, then reinstalled software using the disc images or downloaded again from the supplier (not copied apps off the backup) then moved folders and such over. Just tested both a Lexar and a Transcend and both read fine on a MacBook pro 2011.