Hi, don't panic ;-)
1. You can only do that if you have a free slot. If I remember, there are only 5 slots on left side of the taskbar. So remove one and put QGO in place of it.
Else you can use the second solution and for example use Horizon feed as your shortcut
2. What do you mean by ADB isn't registered ?
4. When you use the second method, this should open this settings window :
What do you mean by the mobile phone settings ? The settings you can see here are Android settings, yes on your phone this is the same app. But as your Meta Quest is and Android device, it has the same settings.