Submerging the sphere gives you the volume. You’re thinking of the legend of Archimedes who measured volume this way and measured mass with an ordinary scale and deduced the density from those two values.

Sketchfab is well-known in 3D rendering and gamedev communities. I don’t think it has many print-friendly models.

I use KDE Connect. Works well with Tailscale when I’m outside my home network.

Thank you, you brought up a good point about them selling data. What alternatives do you suggest to expose my service to the internet for personal use away from home?