I used the hinged wall mount by sozman (https://www.thingiverse.com/thing:4921670) to create a Pi 400 ceiling mount.
In the current times it's not always easy to get your hands on a Raspberry Pi so I use my Pi 400 as my OctoPrint Server and I needed a mount for my Ikea Lack Enclosure.

For the screws I used 4x 4,0 x 30 mm Torx.

The Pi sits in place firmly but can be easily removed and there are no accidental button presses.

No need for support, just print it in place. Very easy to print, I used orange PLA.