Hi Peter,
Blender 4.0 will introduce quite a few breaking changes (also Python changes). You can have a look here: https://wiki.blender.org/wiki/Reference/Release_Notes/4.0
I am sure that a MultiBall 4.0 Rig will be made available, but until then, maybe stick with 3.6 for the MultiBall exercises, or use the Rig without the complete Rig UI.
