Why didn't Wakanda use their jets/ships, specifically to destroy Thanos' army as they came through the gap in the shield, and generally in the battle?
They appear in a few scenes during the battle of Wakanda, presumably having been held in reserve while the close fighting is taking place. They do make an appearance when the subterranean wheel things erupt from the ground.
You see them picking off larger targets a few minutes later
And attacking the drop ships a few minutes after that