it hosts static site only and if thats what you need you need i think you can use wordpress.com or meduim.com or https://teletype.in/ or https://telegra.ph/
but i think it would be helpfull if you mebtion why you wanna make website
It should be possible to create a static landing page using github pages, and then use cross site requests to capture the leads; but then again...
Where would you host the backend? Github only hosts static sites afaik.
With that, your code is public if you host there (html is public, anyway.. for that matter).
It's not such a good idea.