The source of the DisplayPort signal is the Tiger Lake CPU. I suppose there’s probably Intel documentation for the CPU that might describe its integrated GPU and its integrated Thunderbolt4/USB4 functionality.
With Thunderbolt 4/USB 4 functionality, you also get DisplayPort Alt Mode because it’s exposed as a Thunderbolt 4/USB 4 USB-C port. I don’t think Intel makes anything that includes HDMI Alt Mode, so adding that would require some extra chips and take more space on the motherboard.
From a USB-C port, DP++ (DisplayPort Dual Mode) is not a thing otherwise it would be HDMI Alt Mode. I’ve never seen an example of HDMI Alt Mode. Do you know of an example? Probably, any HDMI output from a USB-C port is using a DisplayPort Alt Mode to a DisplayPort to HDMI adapter (including the Framework Laptop’s HDMI expansion card).
If you look at something like the HP Thunderbolt Dock G2, it has a Titan Ridge Thunderbolt controller which has a DisplayPort output that is connected internally to a DisplayPort 1.4 MST Hub with three DisplayPort outputs. Two of those outputs are exposed as DP++ capable DisplayPort ports. The third port is exposed as a USB-C port that supports DisplayPort Alt Mode. The third port is also used for the docks’s VGA output which disables DisplayPort Alt Mode of the USB-C port when connected. That’s ok since the USB-C port can still be used for USB data. You should be able to connect three 4K60 displays to these three ports (the MST Hub converts HBR3 x4 + DSC MST to three HBR2 x4 SST outputs). The dock’s downstream Thunderbolt port has a separate DisplayPort connection if you choose to use that port (because Thunderbolt can carry two DisplayPort signals) but the Framework Laptop is limited to 4 displays including the built-in display.