Cis is a scientific term, in Latin, as is trans. Cis meaning "this side of" and trans meaning "the other side of". If trans is a valid prefix as used in any context, so is cis.
That is a linguistic equivocation I find uncomfortable.
Cis is a Latin preposition governing the accusative that means "on this side of" as in a river. So, for example, cis fluvium (on this side of the river). It was not a scientific term.
It is now a loan-word used in some scientific contexts.
Some people choose to use/find that the preposition trans (also governing the accusative if anyone ruddy cares these day) resonates with how to describe their life.
Why does that mean I am "cis"? If I have to pick any of them, I am non-binary. But I would prefer just to call myself a woman.
If I am to respect other people's pronouns, I rather feel you should respect my nouns.