There are two visually similar sails. Some are rotating tubes that generate lift via the Magnus effect and even though they create low pressure zones, those are not “suction sails”, strictly speaking.

A suction sail is a more or less conventional airfoil that houses an axial compressor to basically suck in air which causes the boundary layer to stay attached which generates lift via the same mechanisms as an aircraft wing.

From a distance and to a casual observer they’re pretty similar.