Turning a perfectly good DisplayPort 1.4 port into a less capable HDMI 2.0 port is always a questionable choice.
...assuming the GPU has the horsepower to drive it at > HDMI 2.0 (or > DP 1.2) rates. Unless Apple have artificially knobbled the M1 Pro MBPs and/or (OK, that
wouldn't be the shock of the century) to only support 2 displays and/or not support HDMI 2.1, they
don't have DisplayPort bandwidth to spare.
And I count up to five Thunderbolt 4 ports on the M1 Pro and Max:
Interesting. I was pretty sure that Apple specifically said that the M1 pro had
an extra TB controller over the M1 - but I see the printed press release just vaguely says "extra TB controllers".
I won't argue with your IC component identification skills - it certainly looks plausible - although I don't get why the "oddball in the middle" would have
two DisplayPort sections...
Also, it's impossible to know whether all of those supposed TB and PCIe controllers can be enabled simultaneously and/or if they are all equal in terms of connectivity to the GPU and CPU. E.g. one of them could be a "runt" just for supplying USB 3.1g1 and HDMI. I'm also thinking of the Intel chipsets which had a bunch of "universal I/O" lanes that could be configured as either USB, general PCIe, SSD-optimised PCIe etc. but only in certain fixed permutations.
...so, maybe the mains-powered iMac will have 4xTB with an extra TB controller enabled at the expense of slightly higher power consumption... or the Mac Mini Pro will have 5 TB ports because it doesn't need to support an internal display... or the iMac Pro XDR will use that "oddball" controller for an 8k display.... I.e. the M1 Pro/Max chips in MacBook Pro, iMac Pro, Mac Mini Pro (...and future Mac Pro?) might be the same physical chips but with different permutations of modules enabled at build time.
Of course, it would be nice if Apple would share this info so we didn't have to speculate, but they do like their secrets.