This is the simplest design for a projector mount, that I came up to. It allows the projector to be securely mounted on the ceiling. It also allows the projector to be adjusted 360° Horizontally, and around 90° Vertically. I am using it in my garden house and I am very happy with the outcome.

The outer part is meant to be mounted on the projector using a default 6mm screw used for most projectors. The inner part is meant to be screwed to the ceiling.

I highly suggest to use a robust material like PETG. Printing is super easy. You do not need any support. Print in both models the base part on the print plate (see Cura screenshot).