Okay, so Steam definitely gives this thing a workout. I've been re-downloading my library, and have noticed that once the install is done my processor drops back down to between 36 and 45 degrees, with occasional spikes to 50 degrees. This is with Chrome open and doing nothing else but browsing. Furthermore it looks as if all of the cores are being given something to do when said download is active, then sleeping once it's finished. So this is normal behaviour for a Ryzen I guess? Panic over nothing?
Not sure if you're are but if you put all your Steam games on a separate drive you just need to reinstall Steam on the C: drive and point it to the drive with all your games on. Just did this myself, saves a lot of time downloading