Neither, Itch or this game have any ads. Not sure what is going on in your end.
Try maybe downloading the game on your PC and then transfer it over to Anbernic.
I found posts from a while ago complaining about this! https://itch.io/t/1075383/ads-on-post-download-popup Today I tried again and it downloaded the game on the first try, so I'm guessing there was something weird on itch's side!! Anyway, I'll try it on my retro-handheld thing and share a photo! ;)