NewPipe is a YouTube frontend (on android), it's like invidious minus the "instance" part, where it basically just grabs the video directly and just plays that. With NewPipe the video still gets views on YouTube's end, I don't think videos watched through invidious count towards the view count on YouTube's end.
Freetube is something that I've seen and/or heard of once or twice; because of that, I can't really say what it is. It's definitely something that is either like NewPipe or Invidious. (I have only heard about it once or twice due to being a Linux user (I use Arch BTW) and stubling upon it's github repo.)
I really only ever watch YouTube on my phone and because I'm an Android user, I have heard of NewPipe and been aware of it for quite a while. Invidious I know about for kind of the same reason. There's an Android app called LibreTube that is basically a frontend for Piped. (Piped is either an alternative to Invidious or is an instance of Invidious, or just straight up uses Invidious as like a backend. Don't entirely remember)
Yep, all front end or services.
Also, I recommend giving Linux another shot. There are many distros that work as expected out of the box; The primary one I recommend is Nobara. Nobara is a Fedora based distro made by GloriousEggroll, the same GloriousEggroll behind ProtonGE and WineGE. It has a custom kernel with additional patches to help make the performance of some things better. It is a gaming focused distro, but that doesn't mean you can't use it for day-to-day tasks.