Right clic to HTML folder, compress -> Here as HTML.zip
Now, you have a file called HTML.zip, that file you have to upload to itch.io.
-----------------------------------------------------------------------------------------------------------
ANOTHER question.
I see that all your files are called "index".
Is the godot project called "index" or did you manually rename all the files?
If you manually renamed all the files, then the game will NOT work. You just have to rename the file that ends in .html and leave all the rest as GODOT gives them to you.