projector screen aspect ratio.

I'm looking to buy a projector and screen. For a projector I'm looking at the Xgimi horizon series Ultra or Pro. I'm new to projectors, & I'm curious about aspect ratios. I know in a 16:9 ratio, it gets black bars on top/bottom. I do know it depends on the ratio the film was shot in. But what ratio are most films shot in to help avoid the letterbox bars?