If I only would need file sync I'd use Syncthing. But with calendars, adresses, chat, mail, decks, etc. I don't know another solution. Some compromises are necessary: I didn't find e.g. a good note taking app with sharing among members. Chat posts cannot be edited.
So far our AIO based installation worked well enough (with PC, Mac and Android clients). But we do not have a lot of files (yet).
After bad experience with incompetent MS support stuff regarding our (not cheap!) Office retail licenses I also had to manage expectations there: a lot of time wasted, they only wanted to move us to the 365 subscription model, could not help. Somehow I'm not convinced that with MS365 we would have a simple well-arranged flexible system (but just be bound forever).
So far our AIO based installation worked well enough (with PC, Mac and Android clients). But we do not have a lot of files (yet).
After bad experience with incompetent MS support stuff regarding our (not cheap!) Office retail licenses I also had to manage expectations there: a lot of time wasted, they only wanted to move us to the 365 subscription model, could not help. Somehow I'm not convinced that with MS365 we would have a simple well-arranged flexible system (but just be bound forever).