The Nebula Cosmos isn't really designed for ceiling mounting from what I can tell. Does it even have the standard 3 or 4 holes on the bottom of it for a universal projector mount?

Anyway, the typical drop ceiling threaded pipe fitting would be the Chief CMA440 which can be had for next to nothing off of eBay.
https://www.ebay.com/itm/225442918903

It sits across the ceiling grid, can be harnessed to the ceiling, and allows for standard 1.5" pipe to be connected with any mount that uses 1.5" pipe. This includes their own RPMAU mount, or the far less expensive QualGear Pro mount...
https://www.amazon.com/QualGear-QG-KIT-CA-3IN-W-Projector-Accessory-Ceiling/dp/B01B1JFMPG/ref=sr_1_4