I don’t know if this issue has been resolved (I’m still running a 2017 Quad-core Intel iMac and haven’t made the switch to M1 yet) but from what I’ve found, basically all Macs need to run UE4 4.19.2. Anything newer than that “locks up” the system. That being said, my iMac turns into a Harrier jet anytime I run UE4.