Not a cure but Rogaine has worked for me. I've always had a full head of hair and for years my barber has commented on how thick it was. After the pandemic, I noticed I had started to lose the hair on the top of my head near the crown. Not much, but it was happening. About six months ago the spot had grown to a (mostly) round patch about 2" in diameter. I wasn't completely bald there but whenever I got out of the shower with wet hair I could see in the mirror there was a bald spot in that area with extremely thin hair barely covering it.
Time to nip this in the bud. My dermatologist recommended Rogaine, the foam, not the liquid.
I spent $60 on a three-pack of Rogaine aerosol cans and started using it on January 1st. By mid-February I could see some progress, not much, but progress. By the end of March there was noticeable fill-in of new hair. Now, in mid-May, the spot is barely noticeable.
A can is supposed to last one month. You apply it twice a day, morning and nighttime, using an amount equal to about one-half of a shot glass (it comes out of the can as a foam.) I ended up getting almost two months out of each can. I'm on my last can now and am only applying during the morning after my shower. You're supposed to apply twice a day, but I have a hard time finding any bare areas to apply to, so I just put it on once a day where I remember the spot had been forming.
I'm quite amazed at the results. I will likely continue using once per day after my last can is finished.