If someone posts their source code publicly, it's open source.
Uh, no. That's called "source-available". Terms have meanings. And from the day the words "open source" started being used, this definition is what defined them: https://opensource.org/osd
You can't just redefine an established term because it's inconvenient to your argument.
It's unreasonable to ask them to review and maintain every PR
Good thing being free/open source doesn't require that, then? It basically just requires the users be free to make their own modifications and distribute them. No requirement for public development involvement at all, really. It's standard practice but by no means necessary.
If you want to fork it and make changes for yourself, you can
They can terminate your license for any reason or no reason (stated in the license) making your fork in violation of copyright law :).
In other words, they can take down your fork if they feel like it. Making the ability to fork useless.
literally the only qualification for something to be open source ...
Again, terms have established meanings. See above.
It's also unreasonable to be upset if they tell you you're not allowed to take their work and re-sell it for your own profit.
I don't see how this paragraph relates to my point at all. Is it about the NewPipe paid clones? Because they were illegal anyways (copyleft violation), no egregious license needed.
But as you said, NewPipe is also copyleft, and it seems like you don't have a problem with that. So I don't really understand what your issue is with Grayjay/FUTO.
What do you mean "also copyleft"? Are you implying the GrayJay license is copyleft? Because it absolutely isn't. Again, established term, definition: https://www.gnu.org/licenses/copyleft.en.html
And finally, here's some particularly nasty parts of the license, which funilly enough you don't ever see in free/open source licenses (because they're horribly restrictive terms):
"If you issue proceedings in any jurisdiction against the provider because you consider the provider has infringed copyright or any patent right in respect of the code (including any joinder or counterclaim), your license to the code is automatically terminated."
"We may suspend, terminate or vary the terms of this license and any access to the code at any time, without notice, for any reason or no reason, in respect of any licensee, group of licensees or all licensees including as may be applicable any sub-licensees."