There is only one correct option in constructions with singular "everyone", "everybody", "somebody", etc., and that is using the gender-neutral singular pronoun "his". Any other alternatives are colloquial and should be avoided in written or neutral English.
Use of “their” as a genderless singular?
There is only one correct option in constructions with singular "everyone", "everybody", "somebody", etc., and that is using the gender-neutral singular pronoun "his". Any other alternatives are colloquial and should be avoided in written or neutral English.