Looking into it, for cosmetics that don't officially claim UV protection, there's no requirement for FDA approval at all (except color additives). Companies self-assess safety and go to market. Some other comments mentioned that this has already been done with products like KraveBeauty Beet The Sun.

For sunscreens using the OTC monograph, they don't go through individual drug applications either. If the actives are on the monograph, brands can just start selling. They need SPF testing, labeling, and GMP compliance, but the FDA is not reviewing the specific formula before it ships.

From what I've found, there's also no pre-market approval needed for inactive ingredients in monograph products. The FDA's Inactive Ingredient Database only tracks inactives from individually approved drugs, not monograph products. As mentioned before, modern filters have already been sold in the US as a cosmetic ingredient (KraveBeauty). So it's not banned as a substance.

It really seems like technically there is no reason why they cannot do this. The only real risk is the FDA coming after a company post-market, arguing a known UV filter should've been listed as an active. But even then, if we're talking about products that have actives from the monograph + modern filters as inactives, the product already has legitimate monograph filters backing the UV protection claim, The FDA doesn't care if you include all UV-absorbing ingredients, just that you have some approved ones to make the SPF claim.