That doesn't make sense, the GitHub repo is still up (in fact that's exactly what you're linking to). A DMCA/C&D targeted at github would have the repo disappear immediately until MS lawyers figure it out -- see the youtube-dl situation. Judging from this issue comment C&D was targeted at nitter's author and nitter.net operator, zedeus. The reason he shut down the instance immediately is because the Netherlands, where it is hosted and presumably where he lives, is very much part of the US (and thus epstein class's) sphere of influence. So are all the other countries where third-party instances were hosted, so it's understandable that their hosters are also afraid of C&D's and shut down their instances (e.g. https://nitter.catsarch.com/).

I'm talking about spinning up instances outside that sphere of influence. A person living in Russia won't give a fuck about any letters from Musk so they can host an instance with no fear (at least in that regard). Russia, despite its crackdowns on internet privacy and freedom of speech in many ways, has been a haven for all sorts of cool piracy-adjacent stuff, so this seems quite fitting.