Frankcesca You are seeking absolutes or assurances that cannot be given. Most claims are worded very carefully, they don't claim actual UV protection in SPF terms. Some products are only for use afterwards and we all know you cannot permanently repair dead hair.
Shea has a very low SPF of 2 or 4 or suchlike, antioxidants can help reduce one aspect of UV damage in living skin but are not deemed to have an SPF. Antioxidants would have to be applied frequently anyway because hey get 'used up' or broken down, as do all chemical sunscreen agents.
I don't see how you would apply enough of any product to get really worthwhile benefits without having hair glued to your head. IMO there is no substitute for covering the hair with a close weave hat or UV Buff, sorry.
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.
CO-wash: Inecto coconut
Treatments: Komaza Matani, coconut oil, Hairveda Sitrinillah
Leave in: Fructis Sleek & Shine (old), Gliss ultimate volume, Inecto argan
Styler: Umberto Giannini jelly, Boots Essentials gel
Experimenting with: going back to basics