i have a Oneplus 9 pro chinees model, that have an Indian ROM installed in it, when i upgraded form Oxygen OS 11 india version to Oxygen OS 12 india version my network cell is gone and i cant make a call or SMS just i can receive calls and SMS,
what I do first,
1- i install an Oxygen OS
11.2.2.2 europe version by using MSM tools
2- then i update to to Oxygen OS 11.2.10.10 from my phone (setting -> System -> Update).
3- I download Oxygen OS 12 europian version from (
https://www.xda-developers.com/download-oneplus-9-oneplus-9-pro-android-12-oxygenos-12/ ) then i installed it by using local update from my phon.
4- after installation of Oxygen OS 12, i have no problem to this moment, but in my city we haven't 5G to confirme you the working of 5G network