We know for sure China is giving what US calls "non-lethal aid" to Russia via trade. We know for a fact that Russia is getting small stuff like bullet proof plates, MREs, gun sights, radios etc. Probably more critical stuff like chips and small engines too. All of them more or less contribute to Russian war effort.
While we can here discuss things like does this thing count as lethal or non-lethal aid, and if a UCAV is lethal aid what about its demilitarised version, or if it's parted out does that still count as lethal aid. However that's not how it works between countries, there's no court or lawyers between countries to determine this. Instead if you got the hard power to back up your words you can just accuse the other guy of something with the flimsiest evidence and the other guy can't do anything about it, as we've already seen with Iraq.
So does the US at this time want to rally up their allies to enact sanction on China? Probably. The lethal aid thing is just an excuse. The fact that they are now saying there's no evidence is not actually relevant because lethal aid was an excuse to start with, rather the no evidence I think shows the hard power to enact this global sanction is not there.