Tap the link. A link of the form api.0xr.space/s/ followed by an id opens 0xr.space, which loads the model straight into the viewer with the scale and display style the sender had. On a Meta Quest or an Android phone with ARCore, press View in your space to put it in the room. No app and no account are needed, and a copy is kept on your device, so it opens again later without the link.
If the sender's upload is still running, the page waits up to 90 seconds and says This model is still on its way from the sender. A link expires 30 days after upload; after that the page says This shared link has expired, and only the sender can make a new one. A copy already kept on your device still opens.
No. The Quest browser opens the link. The free Model Explorer app on the Meta Horizon Store opens the same models; press Scan there and look at the QR code instead.
The sender's upload has not finished. The page keeps checking for 90 seconds. If it gives up, reload a little later, or ask the sender to keep the page open until the upload completes.
Yes. Share on its card sends the same link, which expires on the same day as the sender's.
No. Opening a link downloads the model; nothing of yours is sent.