So, just for fun, I decided to try updating my laptop to use Ubuntu 22.04.1 LTS. Naturally this broke a lot of things, one of which was GNUAstro. I re-installed it successfully (version 18, the latest one I could find in my inbox), but there's apparently a critical issue involving the path to a particular library.
When I run astnoisechisel from the command line (or any other GNUAstro utility), I get this:
$ astnoisechisel: error while loading shared libraries: libgit2.so.28: cannot open shared object file: No such file or directory
Ubuntu 22 favors something called "snap" for certain applications. That particularly library file is here on my system: /snap/gnome-3-38-2004/115/usr/lib/x86_64-linux-gnu/libgit2.so.28
So it seems that even after a successful installation, GNUAstro doesn't look in the /snap directory for some necessary libraries, and so throws that error.
Also of note is that I needed to do sudo ./configure to install this time, otherwise it couldn't find the CFITSIO libraries even after pointing to the right paths. I don't recall having to do that before, so likely that's another Ubuntu 22 quirk. I suppose explicitly pointing to the Anaconda CFITSIO files could work, since those are all in my home directory, but I didn't try.
Personally, I may re-install version 21 (22 also uses Wayland, which doesn't play nice with my external monitor in my office or with IPython), but for those braver than me, those are some of the issues I found trying to use GNUAstro with version 22.