In addition to other people’s comments, flatpaks are usually more up to date than their apt counterpart (expecially those from the debian stable repositories).
I run debian and I deliberately installed some software from flatpak (eg. Ardour and Guitarix) because the deb package is a whole version behind.
Writing from a 3 years old 4a running CalyxOs: the phone is a perfect choice if you want a small sized phone with a 3.5mm jack and that gets constant updates. The camera might be a little better but I don’t take many pictures so I don’t mind.