You are not alone and actually your symptoms sound very similar to mine.
The balloon procedure did not help me. I considered hyperbaric oxygen, but since it is pressurized my doctor was afraid it might make things worse. Like you, I already feel so much pressure in my head.
I also have blurry vision and terrible digestion. Problems I never had before Covid.

I wish I could tell you something that has helped me, but no, nothing has been found.
I will certainly post if I find a therapy that gives ANY relief at all.