There's currently plenty of 3rd party VESA mounts for Mac Mini, I'm sure they'll have some for this new Mac Mini as well. They slide down into a "clamp" style bracket. They run about $15 on Amazon.
You can get 'sandwich' enclosures that put the mini between the monitor arm and the monitor itself, or off to the side. That's what I do with an M1 Mac Mini sitting next to me. Maybe it's a blessing in disguise since you can get these cheaper than what Apple would sell them for :)
A box that small can be mounted with double-sided tape or velcro.
No surprise there; even their monitors’ VESA mounts are optional :D