I’d love to be able to adjust line spacing in the body text of posts, like I’m able to do for the comments. Also, now that I’m writing this, I’m noticing that it would be nice to have that in this reply composition screen too. But maybe I just haven’t found that one?
Sounds likely to be a scent issue - Noki may have gotten the scent of another cat or animal on him which is confusing Scooter.
The steps you’re taking are good and might take time, I’d stay the course as if they are strangers and take the introduction slowly. In the meantime, there’s a product called Feliway (might be a different name where you are) that is a pheromone blocker, it can really help mute the stressful effects these scents can have. They use it in vet rooms a lot. Comes in a spray or diffuser, might help you.
Good luck, I hope it resolves quickly!