You wrote something. Actually wrote it.

But some know-it-all tired of wading through AI-generated slop decided that it was made by a machine — maybe you forgot to not use em-dashes!

It’s annoying but it’s a fact of life. And another fact is that you cannot really prove that you wrote it, because you cannot come up with an actual verifiable proof that a sufficiently motivated AI will not be able to spoof.

Oh well. It cannot be done but we are doing it anyway. You can at least assert that it was you who did it, and sign the writing process in a way that would be laborious to spoof (and take as long as it took you to write).