- You put a URL to your self-hosted game on the Itch page
- You upload an HTML canvas to Itch that simply says "Use the link below", so now it's also marked as a brower game
- $$$
Yes it's a hack, but what you're asking for shouldn't be implemented. Itch is not a directory of external links, it has responsibility to keep what it hosts safe for users. And if they add a big POTENTIALLY DANGEROUS EXTERNAL LINK warning no one will play it anyway, so trouble of implementing the feature isn't worth it.