Oneplus 8 VoLTE (Android 11)

With PDC + root:

1. Enable mode:

   adb shell
   su
   setprop sys.usb.config diag,serial_cdev,rmnet,adb
   

2. Open PDC tool:
   • Select Device.
   • Right click currently Active profile → Deactivate → Sub0/Sub1.
   • Right click new profile → SetSelectedConfig → Sub0/Sub1.
   • Click Activate.

1. Reboot:

   adb reboot
   

Without root:

Modify Step 1 to:

adb reboot ftm
adb shell
setprop sys.usb.config diag,diag_mdm,qdss,qdss_mdm,serial_cdev,dpl,rmnet,adb

References:

1. Activate VoLTE/VoWiFi OOS 11(OB1&OB2)
2. VoLTE in latest Android 11 OOS 11 Beta 1 for Oneplus 6
3. Bell, Telus, Koodo and Freedom Mobile Volte and Vowifi Calling Working Update Android 11 Require Root
4. Enable VoLTE & VoWiFi on all devices NO ROOT.