Having been to Cuba several times, and lived there myself, the last time in Xmas 2019, stranded without funds due indirectly to US sanction (I was collateral damage of a kind), I didn't see any evidence of funding from Russia. Actually I thought the people there felt deserted by Russia, despite many people being named after their Russian soldier fathers, I saw none of those fathers, only deserted people. The Cuban government itself has to be credited for keeping most Cubans alive, despite still crippling US sanctions, I would say.

But I did see solar farms, donated from China to Cuba. And still more are being donated now, which gives me hope for both Cuba and China.

Sanctions in my opinion have absolutely no good use, they are simply an instrument of what has become a passive-aggressive mode of waging very spiteful war, which I hate to say, probably most controversially, is a distinctly female characteristic, as opposed to the old school macho male, who lashes out with overt violence, when all else fails, like Putin / Trump.

Like you say, dissent might be met with explicit violent reaction in Russia, but in US and UK it is met with its own kind of financial sanction, we are "Cancelled", which often puts us into a position of financial ruin, it seems to me.

Are you sure there are no sanctions against China by US? To me, a way of checking which countries are sanctioned, is to see which ones I can do my banking operations from, via VPN. If I try to command a transfer from a chinese VPN, it always fails, the bank refuses to carry it out. If I change the VPN endpoint to a European or US location, then no problem. Further, the areas covered by Amazon, which is under orders not to serve sanctioned areas, show us which areas are sanctioned and which are not. When I was in Cuba, I could not connect to any of my usual Amazon services, hence the reason I had to resort to VPN.