Hi @Juuliuus, welcome to AppImage.
Regarding “modern” versions: I don’t think it’s best practice to assume that all users always have the latest OS version. Hence I want to ensure that applications are built in a way that allows them to run on all still-supported mainstream distributions, especially all still-supported Ubuntu versions. Which for practical reasons means that one should not compile on any system newer than the oldest still-supported Ubuntu LTS. (This has nothing to do with AppImage specifically - if I was developing an Android app, I would also want to make sure that it runs e.g., on Android 5 and up rather than just on Android 10 which practically no one has yet.)
Please ask linuxdeploy related questions in https://github.com/linuxdeploy/linuxdeploy because its author doesn’t read here.
Thanks!