That cannot be true, when I install e.g., Ubuntu system, there are plenty of applications installed for me, with incompatible licenses.

Can you please elaborate on what you mean?

Ubuntu does not aim to be a permissively-licensed system. It can include copyleft (e.g. GPL) and permissive (e.g. MIT) without issue.

Permissively-licensed systems like FreeBSD and GrapheneOS cannot include GPL code if they want to remain permissive.