Export the sketch to Cloud from Gravity Sketch's export menu, open app.gravitysketch.com in the Quest browser and download the file from My Files. Then open 0xr.space in the same browser, press Open and choose the file. OBJ, binary FBX, IGES, glTF and USDZ all open, and the sketch can be turned, cut through, pulled apart and placed in the room. Model Explorer needs no account and does not upload the file.
Gravity Sketch's own .grs file does not open; export one of the formats above. On a standalone Quest, Gravity Sketch sends FBX to Cloud only, and its own documentation reaches a local export through a computer. Downloading from Gravity Sketch's cloud needs your Gravity Sketch sign-in. A model is held between 10 cm and 10 m on its longest side, so a larger sketch is shown scaled down.
Not for Model Explorer: opening a file needs no sign-in. Getting the export out of Gravity Sketch's cloud needs your Gravity Sketch account.
Any of OBJ, FBX, IGES, glTF and USDZ opens. An OBJ needs its .mtl chosen with it for its colours, and an FBX must be binary, not ASCII.
No. It is Gravity Sketch's own format. Export the sketch first.
Not by Model Explorer. The file is read on the headset, and nothing is sent to a server unless you create a share link yourself.