There’s also this Ukrainian report on the matter but it’s in Ukrainian, so I’m sharing the Mastodon post in English.
The US has extensive sanctions against Russia and Putins associates and many violators have already been prosecuted.
The US has specific sanctions against Ramzan Kadyrov and if Musk violated any of them he could be prosecuted for sanctions violations.
That would be separate from a prosecution under “succor to the enemy”. As near as I can tell, that only comes into effect under the very specific case of declared wars and that sanctions alone, aren’t sufficient.