As someone else noted, GP is just misunderstanding a frankly confusing subject. There are essentially two common ways for people to specify their pronouns.

Some people desire a single set of pronouns, and indicate this using the nominative/accusative pair (she/her, they/them, ze/zer).

Other people accept either of two different sets of pronouns, and indicate this preference using the two nominative forms separated by a slash (she/they, they/he, and apparently, it/she).