Russia has military bases and radar installations in Belarus. What are you planning to do about them? Have NATO shoot down Russian aircraft over Belarus?

Ah, I meant from allied states. You'd probably refuse entry to planes that went directly Belarus airspace -> Russian airspace -> allied airspace as well, but you don't have the ability to deny Belarus airspace -> Russia airspace.

Poland is apparently really mad about this, and given that Ukraine is currently at war with Russia you can probably get them on board. Just those two are a pretty good "wall". Maybe add in a few states blocking northern routes (Lithuania, Latvia, Estonia), or not as effectively (Germany, Denmark, Sweden) and they're really isolated from everything apart from Russia.

Anyways, idle speculation, I'm definitely not an expert on this type of politics. I'm sure that in reality a move like this would have all sorts of consequences that I can't predict.