Newbaru

I'm trying to gauge how much actual off-roading newer Subarus can handle. At what point is a 4x4-type locking diff necessary. I've seen pictures of guys fjording, running in deep snow, climbing etc., but wasn't sure if the cars had been modded (drivetrain, not suspension). I understand the basic idea of transferring power to the wheels with grip, but what about in situations when all the wheels are slipping (like in mud)? Are you just stuck at that point with wheels spinning, or does the engine kill power to all wheels? Sorry for the rookie questions. Just trying to figure out what's ahead. Looking to get a newer Outback as a family hauler, but fairly serious MT. bike trail car. Thanks in advance.