I didn’t want to move anything or make any partitions until I got some feedback…but I found a FAQ that said:
Q: Why do I get an error message when I launch Final Cut Pro 7 saying it is incompatible with Motion 5?
A: After installing Motion 5, you need to launch Motion 4 and then close it again to make this error disappear.
It worked. FAQ is here:
https://www.digitalrebellion.com/blog/posts/final_cut_pro_x_frequently_asked_questions.html