I don’t really know the legalitys, but there’s a few things in elons way:

1. Whoever has control over Lemmy would have to be willing to sell it, pretty sure Elon couldn’t take over lemmy like he did twitter
2. It’s open source, how/can does one even turn something like lemmy closed-source?
3. If it was made closed source by Elon, what of the forks that already exist? Can anything be does to threaten their ongoing existence?

I don’t know the answers to 2&3, but I’m pretty sure 1 holds true; Elon can’t buy something if the owner refuses to sell.