I think it's easier to protect skin with products, there are high factor physical sunblocks - AFAIK
you can't use titanium dioxide or zinc oxide on hair, most people don't use anywhere near enough on skin either. Of course skin is alive so can self-repair some of the damage.
There are some cute UV Buffs, have you looked at them? Even if you just used that on the hottest/ brightest days that would make a difference to your hair. Or sit/ stand/ lay/ workout in the shade, or used protective styling some days, perhaps half ups so the vulnerable canopy has some protection. It doesn't have to be all-or-nothing full sun exposure or constant protection, even a 50% reduction would be beneficial.
Long coconut oil soaks helps protect hair from *some* of the UV damage, but I don't suppose you want to walk around with greasy hair. Polyquat 59 can also be useful.
Polyquaternium-59: Sun Protection for Your Curls
2a-2c, medium texture, porous/ colour treated. Three years CG, growing out mechanical and chemical damage = breakage and very high porosity. Past armpit length heading for waist.
Treatments: Komaza protein, Komaza Matani, coconut oil with sugar syrup. Hairveda Sitrinillah
Leave in: Fructis Sleek & Shine (old), Gliss ultimate volume
Styler: Umberto Giannini jelly, Boots curl creme, Rockin RInglets
Experimenting with: Mega-Tek, Curl Harmony reviver, Elvive Full Restore 5.