This is good news. I wonder how this is done.
My understanding was that the non-Pro M SoCs had two display controllers, and two wires: on the Mac mini, both go straight to ports on the back, whereas on the MacBooks and iMac, one goes to the internal display, and the other to the ports.
Presumably, the M3 still only has two display controllers. But, perhaps they added a third wiring: one port is always connected, and either the internal display or the other port is connected. But for the fall MBP with M3 release, they hadn't finished the firmware in time to actually dynamically switch between the two whenever the lid closes or is opened.