Invidious is an alternative front-end to Youtube, if you do not know what this means, it means that it replaces the Youtube main website with another one, but you still watch videos from original Youtube.
Why should you use it? Well it is simple, it is more lightweight than the original Youtube website and you can avoid all the annoying "features" of the original website, like advertising, pop ups etc as well as the spying.
You can apparently also create an Invidious account and subscribe to channels there, if you really cannot live wihtout that feature, but I don't do that, so I have not tested it. As a bonus you can also claim to be more ethical, because you are not using the nonfree software website from Youtube, though you are still "borrowing" all their content.
Nice extra feature is, you can view a more unbiased version of Youtube, because it will not be personalized for you, but you should not use Youtube or similar platforms while being logged in anyway, so a private window regular Youtube will have the same effect regarding that issue. Having an Invidious account may bring you the personalization original Youtube has, but as said I have not tested it, since I do not need it.
It is always handy to have some alternative ways to use Youtube, because their policies get more and more annoying over time, alternatively you can download the videos via youtube-dl avoiding the front end entirely and watch them on your harddrive, similar to Stallman that does not browse the internet, but has a webserver download the website and send it to him, so he can watch it offline, so his privacy is not violated.
I don't really know what category this is, so I just put it into meta tools.