The 4mm occlusion may be muscosal thickening, but it is preventing the sinus from draining properly; we know because of the word occlusion. This description seems a little different that the 2022 CT which seems to indicate that you have no right frontal (I'm assuming) sinus cavity. The "cerebral white matter mild poorly marginated bifrontal periventricular with decreased density is an incidental finding showing mild white matter changes.
My mom was born without frontal sinuses, which is the only reason I know anything. She didn't know until she was in her late seventies. And that wasn't a problem, but separately her maxillary sinus became completely occluded. Her physicians thought it was a sinus cyst, but a sinus specialist performed the FESS procedure, knowing that it couldn't be a cyst if it filled the entire sinus. It was a fairly simple procedure, but fairly new. All the physicians in the practice crowded into a tiny room to watch the procedure for the first time. https://texassinusandsnoring.com/blog/functional-endoscopic-sinus-surgery/
People with MS usually have a lot a sinus troubles.
Meryw, what I would do is have sinus CT to determine if the sinus cavity is there, if it is blocked and if it could be cleared by a simple balloon sinuplasty or FESS.
I would also follow with the neurologist who speculated about the possibility of MS and who seems to be proceeding with the MRI to look for changes in specific areas of the brain. I hope they are able to rule it out.
I think it's too early to start looking at MS information except to check your symptoms against noted MS symptoms. But if you were to get a MS diagnosis you should know https://www.mssociety.org.uk/research/latest-research/research-blog/behind-headlines-car-t-cell-therapy-ms
I hope you keep us posted on your situation.
Wishing you the best.