In case, you miss it, there is a bookmarklet that you put in your browser and then when you visit the site whose video you want to download, you can click that bookmarklet. Another thing is that it supports a wide variety of video sites and not just youtube, despite the name.

Code: https://git.cloudron.io/cloudron/alltube-app
App store link: https://cloudron.io/store/net.alltubedownload.cloudronapp.html
Docs: https://cloudron.io/documentation/apps/alltube/