That's not strictly correct. If you want to get technical on the language side, the original translations of both words, trans and cis, have been fudged. "Cis" means "on this side" which is not quite the same as "on the same side", and "trans" just means "across".
One way they were originally used was "Transalpine Gaul" and "Cisalpine Gaul" to denote which side of the Alps each bit of France was. The Alps themelves were neither Transalpine nor Cisalpine, they were just Alpine!
But these words were used to describe two things (the Alps and the parts of Gaul) that presumably the people using them agreed both existed.
It wouldn't make any sense to describe a part of Gaul as Cisalpine Gaul if the Alps didn't exist and the land was in fact flat, as Cisalpine would have no meaning if there was nothing to be on this side or on the other side of.
However, if one set of Gauls in this hypothetical flat region of Gaul wanted to keep certain other Gauls in their place and make sure they didn't speak out of turn or get involved in Gaul matters and enforce their own rights, they might see a benefit in telling everyone that the other Gauls need to get back in their box because there is actually a big group of huge mountains in the way that will prevent them from attending Gaul meetings that affect the decision-making for the whole of the Gaul region.
The sidelined Gauls say "don't be silly, there's no mountain, I've every right to speak at the meetings and I'm coming", but then the Gauls that are asserting their dominance start defining themselves according to the mountains they say exist that no-one else can see. So they call themselves Transalpine Gauls, and so you can only refer to them by acknowledging that they believe in the Alps. Fine. Makes sense. But then, despite the silenced Gauls disputing that the mountains exist, the Transalpine Gauls, because they've been shutting the other Gauls who disagree with them out of the meetings, decide to refer to the silenced Gauls as Cisalpine Gauls. And so now everyone is referring to the silenced Gauls in terms of the imaginary mountains, the belief in which is the very mechanism that's silencing those Gauls.
And then people will only listen to the silenced Gauls talking if they accept the name Cisalpine Gauls, meaning that those Gauls can only get a seat at the table if they accept the bloody mountains exist even thought they know the land is flat and that it's only the perpetuation of the fiction of the mountains that's impeding their rights.
It's all very galling.
I know nothing about the politics of historical Alpine regions so apologies if I've misinterpreted what these terms mean, but my point is that "on this side" and "on that side" only work to describe a relationship between two things - it's not the word "cis" that's the problem, it's that it's seeking to describe something that only makes sense from the perspective of a believe in gender identity. If you don't believe in it, you're describing a relationship between one thing and nothing, which makes no sense.