[KevinH]

Sigil runs on Catalina just fine. You just need to figure out how to tell the OS that you truly want to open it. Once you do that it works like normal. Depending on your settings, this can be as easy as right clicking on the Sigil app and choosing open twice in a row.

And no, what Apple is doing to try to "control" open source software is misguided at best and truly horrible at worst. Especially since I already pay Apple money just to digitally sign the executable for a "free to all" project and have been doing that for years now!