GitHub link to Nintendo's claim - all the details you need are here
The emulator forks which are being taken down are as follows:
Despite this, the one fork that continues, and will continue without takedown is Ryubing - by Greemdev. This is created by an original member of the Ryujinx team. It's safe, the code is beyond reproach (and violates zero laws or Nintendo code) and actually brings helpful updates.
Still...shitty news. And more indication that the Switch 2's architecture will be damn similar to that of this current Switch. Them taking emulators down means the upcoming games have a solid chance of being emulatable on release. But...that's my own (and others') conjecture, so we'll see when the time comes.
how is pirating games legal?
yep. why? do you understand the only reason people get an emulator is to pirate roms?
Emulation itself doesn't constitute piracy.
Now, it does facilitate it because all you need is a ROM from any source.
However, saying emulators should be prosecuted for it would be the same as arguing that Steam's Proton should be banned because you can launch pirated games through it.
The real perpetrators are those who distribute pirated content. But going against those would be much more difficult, so they target emulators instead.