Export the scan as a GLB, or as OBJ, USDZ or a PLY mesh, open 0xr.space on a Meta Quest or an Android phone, press Open and choose the file, then press View in your space, then Scale and 1:1 Size. A scan made with a phone's depth sensor is in metres, so it then stands in the room at the size of the thing you scanned. The file is read on the device and is not uploaded.
The size comes from the scanning app. A GLB or USDZ says its unit; a PLY or OBJ has none and is read as metres, which is what scanning apps write. A scan exported as a Gaussian splat opens too, as a splat rather than a mesh.
Its texture lives in a separate image named by an .mtl file. Choose the .obj, .mtl and images together, or a ZIP holding all of them.
At the size the scanning app wrote. A phone LiDAR or depth scan is close to real; a photo-only scan can be off, and you can scale it by hand.
Yes. .ply, .spz, .splat, .sog and .ksplat splats open and are drawn as splats.
No. It is read on the device, and nothing is sent to a server unless you create a share link yourself.