Open the Meta Quest browser, go to a model page on this site, and press Enter XR. The model appears in the room with you. There is nothing to install: the headset browser already supports WebXR, so a URL is the whole delivery mechanism.
This is worth saying because the usual answers are not that. Viewing your own 3D files in VR normally means buying a viewer from the Meta Horizon Store or sideloading one through SideQuest, and both of those are an install before you have seen anything.
No. The Quest browser supports WebXR, so the page enters an immersive session by itself. There is no Store app and nothing to sideload.
It runs in the browser, so it works wherever the Quest browser supports WebXR. Passthrough quality and hand tracking differ by headset, and heavier models will run slower on older hardware.
No. A file you import is decoded and stored on the device by the browser. Nothing about it is sent to a server unless you deliberately create a share link.