You can use at least 5 methods to perform the installation :

Via an Android Smartphone (1 possibility)

1. BUGJAEGER Android mobile app (tutorial (EN), tutorial (FR))(download app)

Via PC or Linux or MAC (4 possibilities)

1. Install with the Installer + Instructions (PC and Linux only)(in the download section)
   
2. Meta Quest Developer Hub (MQDH).  It is easier to use than SideQuest and you can drag and drop an .apk and enable ADB Connection with only one action with this tool. You can see all your installed apps, manage images, videos, take screenshots and see metrics, view log and run command in the main screen.
   
   
   
   
   
3. SideQuest (Advanced Installer) (If SideQuest block the installation (safeside), use another solution)
   
   
   
   
   
   
4. Install with ADBLink. (Accept popup in the headset)