Ok so apparently AniYomi is a thing,all it needs is a few modifications
Free OpenSource Software
A group for FOSS enthusiasts sharing news and projects on Free and Open Source Software and Operating Systems, including GNU/Linux, Android, applications, and more.
Why are we not talking about NewPipe?
Because NewPipe as it is right now is restricted in it's reach & somehow GrayJay functions eventhough Newpipe gets blocked by Youtube.
Also NewPipe already exists
NewPipe works perfectly most of the time (including right now). When you say "restricted", you don't mean the age restriction, do you? Because I think those videos indeed don't work in NewPipe. (YouTube sometimes blocks GrayJay, though, don't they? Also, do age restricted videos work in GrayJay?)
Also, why limit yourself to stuff that already exists?
Whatever the case, if you're looking for a FOSS alternative to GrayJay, NewPipe is exactly the thing that most serves as an answer to your question.
Restricted as in I cannot add more plugins for other platforms & comment.
Maybe try not burying the lede next time.
Whatever the case, NewPipe is still a "serious attempt ... on creating a truly FOSS alternative to GrayJay app" (except I'm pretty sure NewPipe predated GrayJay), and it's by far the closest thing to what you're asking for. They seem broadly open to the idea of adding a plugin system to NewPipe.
I actually didn't know about this (Plugin system), thank you.
FWIW I had my reservations about the "source first" licence grayjay uses as well, but I'm impressed by the FUTO org's principles, how they respond to bugs, how fast fixes and improvements come, amount of sponsoring other FOSS projects they do, etc. Plus Rossman's work for R2R and other generally good ethical behaviour. So I believe their reasoning when they say its necessary.
I ended up purchasing the licence and am happy with that decision. I just look at it as a donation to support the development, and the fight against big tech which would have happened if it was FOSS too in my case.
Also the best/only source available app to access nebula.tv content AFAIK 🤷♂️
Who the hell disliked this & also I want to know more about Source-First from your POV
Who the hell disliked this
That was me. I think FUTO is basically Satan, only less cool. I go into the reasons in this comment.