Still not a pro in making money, but I'd imagine the mindset for this is similar to running ads for small businesses: do you see something in the business that is weak, and if you fix it, can it increase revenue/ save time enough to justify them to pay you a retainer? Run funnels for people to join their Onlyfans? Help them create a product independent from Onlyfans? Use Zapier to automate shit? Only you can answer that.
Personally, I don't wanna do that because I don't wanna desensitize myself to girls' nudes managing an account. But I can see that it can be lucrative, if you know their market, their pains, and ways to make them win more.