Rear derailleur movement where it is bolted to hanger
I think you cannot do anything with this wobble. I have similar one, opened the derailleur, but inside I just found out that the part that goes around that bolt inside is probably slightly deformed. It is a metallic cylinder - a hole that goes around the bolt, but when it becomes deformed to be slightly wider, it just causes some play of the derailleur on the hanger.
You can test whether my description fits your situation by wiggling the derailleur and looking what actually moves. In my case the bolt and the flat metallic part connected to it stay firmly connected to the hanger and what moves is the actual body of the derailleur (painted).