Yeah, I think it was just compiled on a Linux with a newer version of glibc than is available on Ubuntu 20.04. I know for a time the official Godot Linux builds were done on a older Ubuntu (maybe 16.04?) to prevent this issue, but now I think they are done on a fairly recent version of Fedora, so there must be some other way around this problem. I do custom Godot builds for some of my games, and I use the same Docker containers as are used for the official builds, and it seems to work out.