There is an app on android called Video Downloader to pirate videos from websites. Now, it works for almost every website except youtube. The problem with this app is, it has no adblocker and when you visit sites you should not visit without an adblocker, it just rains ads on you. So, is there a website equivalent of this app which can download videos from any website?
If the only thing you are missing is youtube download ability, why not use one of the many options to do that from a handset? Newpipe or Spottube are on fdroid. https://invidious.io/ allows you to do it from a browser.