It's not that hard to release a Web game at least from my experience
All you have to do is:
1. Export the game
2. Change the HTML file's name to index, Or whatever that it asks for.
3. You send it to Itch.io as if it's a normal game, And then you pick from the categories of stuff like "Soundtrack" or whatever, to... web? or something? I dunno I'm saying all of this from memory.