Hi Andrew,
I run a bit of a particular system, Fedora Silverblue (BaseCommit: 937a5ecc6e9ea48640023eb51299f7256926f8f69a800af1def3397219cbd33c) with the guix package manager ontop (which puts things in locations outside FHS). Not sure this is worth debugging.
The first command got me:
U ZSTD_compressStream2
AppImage typically depends on the host libraries for anything not packaged. This fails on weird systems. In the AppImage I generated for my entry I packaged all dependencies (which inflated its size) in the hope that it will work for more people.