do you mean languages that don’t distinguish plurality in third-person pronouns?
i’m not sure but WALS lists nine languages as not having plurality in personal pronouns: pirahã (of course lmfao), burmese, canela, oneida, maricopa, cocopa, and kiowa (they’re the gray circles on the map).
i have no idea about the accuracy but wikipedia describes burmese pronouns as being able to take a suffix, -tui., to show plurality. for example su “he, she, it (they ?)” > sutui. “they.” so there is a mechanism to make a third person pronoun plural, even if it’s optional
wikipedia also describes pirahã as not having any plural pronouns as a basic morpheme, but instead using compounds of other pronouns, such as ti3 gi1xai3 “we,” literally i [and] you. it also says that there is (at least according to steven sheldon) a plural third person pronoun that may be restricted only to humans. sheldon writes it as hi3ai1ti3so3 “they (human?)” which i have a suspicion is a compound word — ti3 means “i, we;” hi3 means “he,” ai1 seems similar to the second half of gi1xai3 — but i really don’t know
from veryyyyyyy quickly skimming this teaching grammar from u wisconsin green bay, oneida seems to prefer pronominal prefixes on verbs rather than independent pronouns. the pronominal prefixes seem to distinguish number and gender (pp 19-20). however, independent pronominal forms do not distinguish number in the first or second person (íˑ, níˑ, niʔí for “I” or “we,” íˑse, níˑse, niʔíse for “you”). independent third person pronouns is generally only né regardless of gender or number, but more specific terms exist to clarify — laulháˑ “he;” akaulháˑ “she;” aulháˑ “she/it;” lonulháˑ “they” (page 120)
that’s what i can find and if anyone knows better please correct me