Its dont exist specifically for html opening, but built with that specific android html issue in mind, like a bonus. Probably devs struggled with that issue themselves, and they built into their file explorer a small solution. Its not even file manager function, it runs custom local http server specifically for html games. File explorers shouldnt even do that, its not a function you would expect. But it does, which is very helpfull. Its a coincidence that you have cx file explorer, and play html games, thinking its built in android function. If you dont believe me, try to download another file explorer from google play store or aurora store and try to play html game trough that.