What about proof, roof, belief?
TERF is an acronym rather than an initialism, and no reason to assume that it would follow the same rule as elf. Both hoofs and hooves are acceptable plural forms of hoof.
Changing the f to a v in this instance makes no sense as the f clearly stands for feminist. Doubly so if you treat it as an initialism rather than an acronym as you would then be saying T.E.R.Vs