As of 2020, no one knows how to build the major desktop distros fully from source into the ISO, and especially so in a reproducible build way. Everything is done in build servers somewhere with complicated layers of prebuilds. It's crap.

Yes:

No:

Ubuntu: askubuntu.com/questions/82302/how-to-compile-ubuntu-from-source-code source: sausage factory

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Package manager

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Cross distro package manager

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AppImage

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Flatpak

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Snap (package manager)

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merlijn.sebrechts.be/blog/2020-08-02-why-one-snap-store/ has some very good comments on how snap is more closed than Flatpak.

Snap's permission system is extremely annoying, notably restricting access to home files. They need a popup that says "permission required by app, accept?" urgently!!!