Watching a movie using a projector and MacBook Pro utilizing a USB-C Muiltiport Adapter and cannot display movie on projector unless the laptop is physically closed. Any thoughts?

Mirroring the display and the projector forces both to use a common resolution. Users occasionally find that one or the other display drops out at that 'compromise' resolution.

When you close the display, the projector is free to use its "native" resolution which works much better and you get a picture.

Turn off Mirroring and the problem will be solved.