In Desktop, when you set up a Relate between tables, it worked in both directions. In Pro, when you set up a relationship, it only works in one direction. It is not a huge deal, but an annoyance to have to start from one table and set it up, and then recreate the relationship on the related table, when you might want to select records in one and see related records in the other table and visa versa...
Can someone please tell me if there was a good reason why this changed between Desktop and Pro?
If you don't get an answer, you could post it as an idea.