snaps are intended for non-power-users that don't want to deal with dependencies. Those users want things to mostly work without worrying about murky downsides. Auto-updating is exactly the right behavior.
If this is of concern to you, why are you using snaps? And why Ubuntu? What's the value-add over Debian?
If this is of concern to you, why are you using snaps? And why Ubuntu? What's the value-add over Debian?