I've wanted to mount my MacBook under my desk and this is what I came up with for it. Locks into place once you connect one of the USB-C Ports closest to the touchpad.
Leaves enough space for ventilation and due to its small size is not on the way while not in use.
Could possibly fit other models of the MacBook but I haven't tested any.
Use whatever screws you have around just make sure they won't poke through your desk.
The author marked this model as their own original creation.