I just tried the link and several other jams in incognito mode and didn't get any ads.
I've never read about anyone reporting anything similar; it seems to be something on your end.
Viewing post in Really annoying ads when not logged in
I just tested it from my Android phone, where I'm not logged in to Itch, and I can confirm that the page is showing me an ad.
It's really strange, because even using an incognito account, I can't get it to show the ad on my PC, so I really don't know what's going on. Hopefully, someone can help us figure this out.
EDIT:
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?
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.)