Hi @t0bi,
There should be no issue running the Pmod RS485 at 5 V; the datasheet for the embedded module (https://www.analog.com/media/en/technical-documentation/data-sheets/ADM2582E_2587E.pdf) even uses Vcc at 5 V (unless otherwise noted) in its Specifications table.
3.3 V is listed in the Reference Manual since all of the Digilent system boards with Pmod Host Ports operate with 3.3 V logic, but there isn't really any difference between operating at either of the two voltages from a pragmatic functionality standpoint.
If you wanted to be technical about it, the Typical Performance Characteristics graphs in the Analog Devices datasheet indicate that operating at 5 V consumes less current than when operating at 3.3 V (based on Figure 3 and Figure 4), but that's at the cost of operating at ~100 mW higher (at least for when I looked at 20 degrees C with an RL of 120 Ohms). Whether that is something you are concerned about in your system I do not know.
Thanks,
JColvin
