This was the situation in the past, but the US has now forced Mexico and Vueneusalia to not ship Cuba gas. Of course the cuban economy is so weak it can't afford solar which could solved this, largely due to their own failures

Even in the past there has been a bunch of nonsense "rules" that made other countries choose between trading with Cuba or the US, but not both.

To name one, if a ship docks into Cuba without filing paperwork requesting to do so from the US, it cannot dock into any of the US ports within 180 days of leaving the Cuban territory.

To name another one, if some product is made somewhere else, but contains >10% of US-made parts or materials somewhere in its supply chain, then as far as the US government is concerned it might as well have been 100% made in the US and therefore cannot be exported to Cuba. Otherwise, the company that sold it to Cuba risks being banned from operating in the US.

So the US is and has been pretty much tilting the scale against any other country in the world trading with Cuba, using its own purchasing power as a bargaining chip.

As for solar panels, they do not solve your inability to move cars around. They do reduce your need for fuel, but when you're 100% out of fuel, no car can move around and no amount of solar panels is ever going to fix that.