This is a custom wall mount for my 2nd screen Dell P2417H (simmilar models with same stand will fit as well). It's a 24" monitor with pivot stand (can adjust up/down, portrait/landscape and tilt), but it doesnt suppport vesa mount (edit: this is wrong, it does support vesa, but then cant use pivot mechanism). I wanted it on the wall so I printed 3 parts out out of PLA. One part is screwed in the wall and the other one is securing monitor in place using zip ties. 3rd part is a small shelf that is mounted underneath (with original screw for monitor base), but its there mostly to provide a flat surface between monitor and a wall.
I've been using it (2 actually) for few years in old place and I love it. It can be a bit tricky to tighten zip ties, but its only done once anyway.
I'll upload files if someone needs them
Buddy of mine has 6 Dell monitors he inherited from a network upgrade that have no VESA holes.