In this video, it is shown how to add WMSService to ArcGIS pro. The WMS used here is a digital orthophoto image service from Geobasis NRW.
This and more online services for NRW can be found here:

https://www.bezregkoeln.nrw.de/brk_i...

There is also a help page to accomplish this task, it took me way too long to reproduce the steps, so I made this video.

The help page can be found here:
https://pro.arcgis.com/de/proapp/hel...