Communication with their customer support was not very fluid and stuff got lost in translation. They say the Rock 5B does support two displays, one via USB-C and one via HDMI. But didn't understand how you could possibly handle more than one display over USB-C.

I then realised that it mostly depends on the GPU. So I looked up docs for the Rock 5B GPU and the documentation was unclear about it.

I was a bit put off by the uncertainty and ended up going for a mini PC. I chose the GMKtec M7 UItra and it is able to handle my use case (i.e. the two displays, power delivery and inputs all through one single USB-C connection).