Okay, my PC isn't showing me the ad because Firefox is blocking Google Ads, but I don't know why that page has that advertising. I haven't read anything about Itch adding this type of advertising, and other pages don't seem to show anything. Could it be something to do with that developer's CSS?
Viewing post in Really annoying ads when not logged in
Yikes.
We should have been made aware if our works are being used for Google Ads tracking and profiling, if pages act as if infected, or if harmful messages are being shown after download to people who don’t have sufficient protection. (To that last point: malicious political campaigns too often show up in Google ads on art websites.)