Well the only Fix, that seems to work for me, was to download the Windows Installer, add that to Steam, and set GE-Proton to v9.16, painstakingly set the correct install path z:/home/deck/.itch, and finish the install
Find the actual installed executable, and add that to Steam, and set it again with Proton 9.16, thennclean up the old installers off SteamOS.
Read the GitHub Cloudflare fix, in the Issues thread, (Google it!), set the correct line of code, and save it.
Then it should work, Again.
Oh yes BTW it would be nicer to use the native Linux version. Alas for whatever reason once you manage to apply the aforementioned fix. It breaks the App from executing inside SteamOS. Oddly enough it works fine under Desktop Mode. But Desktop Mode sucks.
The most direct way (On the StramDeck), is to install the Flatpak off the Discover Store. Two things make that impractical though.
1) It's not supported, by Itch or it's creator anymore apparently.
2) You can't patch it as simply as a direct install beit Linux, or Windows. As any patches, are at App level. And not for flatpaks.