I always felt that snap was designed for servers with desktop being an afterthought (thus why so many things still don't work in snap, ex: sys gtk themes). Flatpak on the other hand was designed desktop first and barely works for server stuff. But the Flatpak experience on the desktop is vastly superior to the snap one IMO.

Actually, snaps inherit from Ubuntu Phone's app packaging mechanism, so it's neither server nor desktop — but certainly closer to the end-user side of the spectrum.

(For server apps, the auto-update mechanism has a really painful consequence, which is that for clustered apps you have a built-in race condition that might kill your cluster)

Often won’t work running something like FRR in a container (and therefore it’s own netns,) because it has to update kernel tables etc.

You can do it in a privaledged container afaik though.