.APK files are for android and mobile VR. Oculus quest uses a different store and game files then Rift and Rift-.s. It is more of a mobile headset. 3dxchat does not have a official apk file. It is a pc game.
There is ways to try and get your pc games to play on the Quest but its really complicated. It May require additional hardware and lots and lots of fiddling, head scratching and research. . You could try the new Oculus link. Or some older methods to get steam Vr games to play. That said, nothing is guaranteed. The game is not supported for Oculus quest. So anything you do try will be on your own.
This is all experimental beta stuff though and requires a unique expensive cable that may or may not work. This is the newest way. there is other ways he mentions in the video to that are wireless and require , riftcat, Virtualdesktop and other stuff. He has some older video's on how to set that stuff up. It is probably possible but expect a whole lot of fiddling, learning through trail & error and some brain farts along the way . Could be all for nothing to. Or it could work. Support will be no use in this regards though for 3dxchat is not officially supported for Quest atm. Better off on the Oculus reddit or official Oculus forums for real technical info and tutorials on this subject.
Hopefully in the near future it will be a bit easier once Oculus releases its official cable and Link comes outta beta. Right now though it seems hit or miss.