Website says it supports 3 6K displays, here you go:
M4 (Thunderbolt 4):
- Up to three displays: Two displays with up to 6K resolution at 60Hz over Thunderbolt and one display with up to 5K resolution at 60Hz over Thunderbolt or 4K resolution at 60Hz over HDMI
- Up to two displays: One display with up to 5K resolution at 60Hz over Thunderbolt and one display with up to 8K resolution at 60Hz or 4K resolution at 240Hz over Thunderbolt or HDMI
M4 Pro (this one has Thunderbolt 5):
- Up to three displays: Three displays with up to 6K resolution at 60Hz over Thunderbolt or HDMI
- Up to two displays: One display with up to 6K resolution at 60Hz over Thunderbolt and one display with up to 8K resolution at 60Hz or 4K resolution at 240Hz over Thunderbolt or HDMI
OK, so unnecessary and arbitrary restrictions on screen numbers, once again.
There is really no reason you couldn't drive four (or more) lower resolution (4k) screens, given the array of ports.
In case anyone is wondering, the use-case here is a triple-monitor configuration at a desk with a much larger "TV" positioned, or hung, elsewhere in the room.
USB PHYs aren't the same thing as display controller IP blocks. It's obviously possible to design a chip with more of the former than latter. At the hardware level, nothing is actually an arbitrarily-subdividible budget of display bandwidth.
The SoC needs to have a hardware display controller for each display, and Apple only put 3 of them on their chip.
You can add as many extra displays as you want using DisplayLink which runs as a standard USB device and doesn't use the built-in controllers, but has worse performance, probably good enough for a "TV" though.
The published specs call out 3 6k screens but is that a display bandwidth limit or an arbitrary “screen” limit ?
I’d like to drive four displays and 4k is sufficient for me … possible? Perhaps with Number four on the HDMI port?