Create ahk_x11
Invalid memory access (signal 11) at address 0x0
[0x55d761e954f9] ?? +94383549011193 in /run/firejail/appimage/.appimage-9683/AppRun.wrapped****
well that's certainly not very helpful. It's possible it doesn't run on Ubuntu 18.04 because I build it on 20.04, but then it should show a dependency error, not a segfault. Anyway building on 18.04 is a pain because I need more recent Gtk3 features and building all Gtk libraries and their more recent dependencies by hand is a huge pain. So I might actually just give up instead.
But whatever it is, I will have to continue this another day, feel free to leave it open or just close it.
Why do you think you need to build on 18.04? (Did I forget to update the documentation somewhere?)
The oldest currently still-supported Ubuntu LTS release is 20.04 LTS. So this is the one to target.
Also, it seems like you are using linuxdeploy and linuxdeploy-plugin-gtk. Please consider asking for help over at https://github.com/linuxdeploy/linuxdeploy/issues in case the issue persists.