I’ve never heard of Macs running embedded systems - I think that would be a pretty crazy waste of money - but Mac OS Server was a thing for years. My college campus was all Mac in the G4 iMac days, running MacOS Server to administer the network. As far as I understand it was really solid and capable, but I guess it didn’t really fit Apples focus as their market moved from industry professionals to consumers, and they killed it.