Easy static link everything.

I think you meant a GUI application that runs on a version of Linux older than yours.

Statically link everything? Including glibc?

AppImage is sufficient.

nope, it still requires at least the glibc version that the appimage was compiled against. snaps, flatpaks nor appimage solve the long-standing glibc versioning issue that plagues portable Linux binaries. the closest I've seen to fixing this issue is https://github.com/wheybags/glibc_version_header

Or just compile against an older glibc version. Plenty of tools to setup sysroots for that, e.g. https://wiki.gentoo.org/wiki/Crossdev