mediochrea: You're absolutely right. We're working with itch.io, Grant for the Web and Coil to try and come up with a solution for itch.io, but if that doesn't come through we would have to ask you to submit games as zip files (and optionally also with a playable link you host yourself). We will update you on this as soon as we know more.
We've added this to the jam page:
"Games should be submitted as .zip archives (with an index.html and all files needed to run the game) and as a link to a playable version of your game with Web Monetization enabled on the page. We are unfortunately not able to use itch.io to host the playable games as itch.io loads HTML5 games in an iframe which prevents a Web Monetization enabled browser from detecting the payment pointer and your game from detecting a paying player."
Although this has already been announced elsewhere on the forum (https://itch.io/jam/the-web-monetization-challenge-2020/topic/1022867/web-moneti...) I thought it best to share it here as well that itch.io has added the "monetization" value to all HTML5 iframes.