Open 0xr.space, press Open and choose the .usd, .usda or .usdc with the files it uses, or the folder or ZIP holding them. Text and binary (crate) layers are read in the browser, with sublayers, references and payloads to other picked layers, and each variant set uses the file's own selection or its first variant. Materials come from UsdPreviewSurface and MaterialX image nodes, with GeomSubsets and displayColor, and metersPerUnit and a Z up axis are applied, so the model stands at its real size.
Only meshes are drawn: USD's built-in shapes such as Sphere and Cube, points and curves are not. Animation and skinning come in as one still pose. A reference to a file that was not picked, a URL or an absolute path is dropped; if nothing is left to draw, the app says the external USD reference is not supported. Textures must be PNG, JPEG or WebP.
The file points at another file that was not among those picked, or at a URL or an absolute path. Pick the whole folder, or package it as a USDZ.
Not in the app. The selection authored in the file is used, or the first variant of each set.
No. Animated and skinned models open in one still pose.
No. It is read on the device, and nothing is sent to a server unless you create a share link yourself.