I just upgraded to ArcGIS Pro 3.5 yesterday (05/13/2025) and found a bug that is a bit of a pain.
All of my feature services in ArcGIS Online (AGOL), which have published relationships, do not relate properly in 3.5. I open the attribute table, select a record and click on relate and nothing happens. Any feature classes that I have locally, all those relates work perfectly.
So to test this, I uninstalled 3.5 and reinstalled 3.4 and all of my AGOL relates work perfectly.
I just wanted to post this bug just in case you are considering migrating to 3.5 and you do rely on doing AGOL relates.
~DJB