What displays work with the Mac Pro (2019)? What displays besides the Pro Display XDR will work with the 2019 Mac Pro? Is there a list somewhere of (both Apple and non-Apple) displays that are compatible?
The new Mac Pro can be configured with a range of graphics card options. 

Regardless of the option chosen by the user, it can be connected either via HDMI 2 or Thunderbolt 3 to compatible displays, and also provides the option for DisplayPort connections*.

The various graphic card options also provide different combinations of these ports. For example, the base level AMD Radeon Pro 580X comes with two HDMI 2 ports and four DisplayPort connections that can support the following combinations of external displays:


six 4K displays
two 5K displays
two Pro Display XDRs


The AMD Radeon Pro Vega II, on the other hand, comes with one HDMI 2 port, four Thunderbolt 3 ports, and two DisplayPort connections that can support the following combinations of external displays:


six 4K displays
three 5K displays
two Pro Display XDRs


And finally, the AMD Radeon Pro Vega II Duo comes with one HDMI 2 port, four Thunderbolt 3 ports, and four DisplayPort connections that can support the following combinations of external displays:


eight 4K displays
four 5K displays
four Pro Display XDRs


Of course, with the expandability of the Mac Pro you also have the ability to use different graphics cards and therefore the types of displays compatible with it will depend on the card you're using. 

Finally, with the use of adaptors you may be able to support other displays as well.

* DisplayPort connections are routed to the system to support internal Thunderbolt 3 ports