I dont have experience from Ubuntu nor snap but a couple workaround suggestions:
(I just tried and QElectroTech_0.8-r7124-x86_64.AppImage do work for me in Mageia 7)
Have you tried other QET versions in Appimage form, i.e 0.9 dev or 0.7 - do they work?
Can you use Ubuntu or Debian packages from https://qelectrotech.org/download.html ?
Do flatpak work for you? (works for me but I dont know if Ubuntu support it)
Next option is to compile it yourself.
That said, yes optimally an Appimage should contain all it need... There was a while the Appimage did not work for me on Mageia, but it got fixed. Also there it complained on GLIBC version https://qelectrotech.org/forum/viewtopi … 8344#p8344