So, I wanted to do a fresh install of Catalina, and have done a backup on my USB drive. Before transferring the data to USB, I've formatted it as "Mac OS Extended (Journaled)". After I've installed Catalina, I can no longer read the data from USB, and receive message: "The disk you inserted was not readable by this computer".
I've tried to read it on my Windows machine using a free program (HFSExplorer), but it couldn't even find my USB drive. I've tried to read it on Linux (Ubuntu), installed "hfsprogs", but couldn't mount it.
I've also tried using several free data recovery programs, but they've managed to recover only data from my previous Linux pen drive installation that I've removed before doing a backup.