The same rules we learned for the M1 and M2 and M3 mostly still apply to the M4 models. Display interfaces are generated deep inside the system on a chip. How many there are depends on the exact type of Processor:
M3 (plain) like the 13-in and 15-in supports up to ONE External fully hardware-accelerated external display.
Except the M3 MacBook Air models with 13 or 15-in display, (and certain M3 plain MacBook Pro models when running MacOS 14.6 or later) which can support a second external display instead of the built-in display when you close the cover on the built-in display. This may require MacOS 14.6 or later.
M4 (plain) supports up to Two fully hardware-accelerated external displays (three for Mac mini)
M4 PRO processor supports up to Two fully hardware-accelerated external displays. (three for Mac mini)
M4 MAX processor supports up to Four fully hardware-accelerated external displays.
M4 ULTRA processor supports up to Eight fully hardware-accelerated external displays
Tech Specs now available here:
MacBook Pro - Tech Specs - Apple
MacBook Pro - Tech Specs - Apple