I would like to have a free (not necessarily) YouTube downloader for Windows (not a website) And I would like to have it adfree too.
3D Youtube Downloader is a windows desktop portable application that can download videos from youtube in various quality settings.
Try youtube-dlp - a fork of youtube-dl with additional features and fixes.
JDownloader is a free, open-source download management tool with a huge community that makes downloading as easy and fast as it should be. Users can start, stop or pause downloads, set bandwith limitations, auto-extract archives and much more. It's an easy-to-extend framework that can save hours of your valuable time every day!
Cross-platform, Mac/Win/nix. Can download pretty much anything you ask it to. Can collect links from your clipboard too, so you don't have to specifically copy/paste to it.
For Youtube, it can download all the individual components that make up the post, not just the video - it can separate out the audio, poster frame, subtitles etc if you want it to.
It's not 100% ad-free, but they take up a teeny bit of the top right menu bar you can totally ignore them & are generally for download sites/structures the app itself enables you to use & save credentials for. I wouldn't really count that against it.