How would you cover this vent?

In my opinion (this is not suppose to be an opinion site) you need to disguise the vents. One way would be to add a large bookcase along the entire wall. This would give you an opportunity to cover the barn door hardware too.

Don’t “cover” the vents. Let them be exposed behind pictures of your cat, knickknacks from your last trip to Greece, books, etc.

I’d move the thermostat out to be flush with the face of the books, but I’d leave the outlet and switch recessed.

Two ways to approach this. If you have the money, you can just have the vent moved to a different location. Just hire a competent HVAC contractor or a HVAC engineer to tell you where you should have it placed.

The second option is to make the seller move it. This will take bit of effort and time. You have to first determine whether that's a supply or return.

Do not rely on a home inspector to tell you. They are a complete waste of money and they really should be illegalized. Nearly all of them have no construction experience and simply take a course to get licensed. You think that a simple course will teach them all the ins and outs of proper construction? An experienced GC whose worked for years will have a hard time knowing everything.

You should turn on the cooling and heating to see if the air is conditioned evenly throughout the entire house, especially with housing units that have multiple levels connected or cathedral ceilings. Think of air as water with hot water slowly moving to the top and cold water moving to the bottom.

With respect to that specific vent, it looks like a return vent meaning the air is moving hot air back to the air conditioner. Supply vents usually have some manual trigger to control the air flow although that is not always the case. To check to see if it's a return, turn on the system and place a piece of paper over it. See if the paper is blowing away from the vent or it sticks to it. If it sticks to it, then it's a return. It shouldn't be next to a window. That's where the supply is.

At this point, you can ask the seller to move it to the middle of the room where it's supposed to be, after getting an HVAC contractor or hiring an HVAC engineer to verify everything I'm saying and stating that it's improper to have the HVAC located there.