This is very multipurpose, but if you haven’t heard of gridfinity, there might be modules that would be helpful you home lab, or your home in general.

I have a 10" width rack cabinet where my Proxmox cluster (three mini Lenovo Thinkcentre) lives. I’m currently designing a 10" mount to hold an old phone so that I can see my server monitoring/status through the glass of the door.

3D printing is great for stuff like that.

Rack-mounted beer holder.

Jk. But really, anything which helps organize stuff is a worthwhile job for a 3d printer. Even something to loop fibre optic cables on, so that they don’t exceed their maximum bend radii, is useful.

I think you’ll also find the 3d printer aids in other endeavors. I’ve used mine to print replacement car trims, ham radio accessories, a photo film spooler, a bushing to convert vacuum hose diameters, and other odds and ends.

One of my friends printed this tiny rack for a small switch and two micro PCs. It’s pretty cute and nifty

Rack mounting non-rack-mount gear always seemed like an interesting application to me. Raspberry pis, tiny lenovos, network gear, etc.

e.g. https://www.thingiverse.com/thing:4769452

Been a few years so I don’t have the link, but I bet you can find this (or something similar) online. If all else fails, I hoard all the files I used somewhere on my nas.

Not home lab specific, but a few things around my house to help inspire you.

Cable fingers

Nuc wall mount

Tool peg board mounts

Heavy ass speaker onto a vesa pole mount to get them above my monitors

Couch gaming gear

Sonos wall mount