I totally understand your concerns, the amount of AI stuff in applications these days is honestly scary.
I've added a link to my Twitter to my itch.io profile. It has some of my older work (even one piece from 2021, before AI). I've also added a link to my website on Twitter, where you can find my contacts. I think this should be enough to show that the art is actually mine.
I'm also fine with doing the first task with payment after it's done, and I can send you a GIF of the drawing process. At least I hope AI can't make a GIF showing the actual process of creating pixel art yet...
Anyway, feel free to message me. There's always a chance we won't even agree on the rates or payment methods 😅