I don't think the processor has an impact, USB-C works perfectly and charges your Macbook Air at the same time. Brilliant screen, but unfortunately it got a bit expensive.
Looks like the U2721EN is an updated version of the same display, adding the LAN port. The "21" in the name indicates a 2021 model, whereas the "19" in U2719DC indicates that it is a 2019 model.
As far as I can see, no (if you also connect the USB-C in addition to the DP, it probably works, but then it makes little sense...). If you don't need the USB-C, as far as I know there is also a cheaper model without it.
I use the monitor through HDMI - PC connection. I suppose you could also connect via USB-c and change the line in. At the same time, I'm unsure, probably you can't watch two channels at the same time.
I have a MacBook Pro and use this monitor. It works fine and teh reason I bought it, is that the battery is loaded also through the USB-C cable from the screen
Only the following parts are included:
Monitor, Stand Riser, Stand Base
1 x Power cable
1 X DP Cable (DP to DP) 1X USB Type-C cable (C to C)
1 x USB 3.0 upstream cable