Looks like tar spots to me - unusual to have that many on the roof but not impossible. Try a dedicated tar remover - Autoglym do a good one (called "Intensive Tar Remover" IIRC) that should have a good chance, it also works well for tree sap (which is another likely culprit).

I finally got these black dots off the roof of my car - I still don’t know what they were from (artillery fungus?) but they made my paint feel super rough and wouldn’t come off with a car wash. I got helpful advice here and thought I’d share what I did in case it helps someone having the same issue!

Tiny black spots on your car’s paint could be a myriad of things, such as tree sap or bug guts. It could also be a certain kind of mold spore called artillery fungus or fallout from trimmings called rail dust. Most of these black dots can be removed with a clay bar, a tar remover, and a polish.

Recently I noticed a few white "spots" on the roof. I tried to buff them out (pretty aggressively) to no avail. It looked like maybe some type of acidic water or something dripped on my roof.

I foamed my car with dawn dish soap to remove any existing coatings from it, then I sprayed the dots with full strength Extra Tough APC and let it linger for a few minutes. I sprayed another patch of them with Gyeon Tar Remover to see if that would do anything different.