So I have some good news, I tried installing GSI image of Phh AOSP:
Flashing procedure for OnePlus 7 (guacamole) Indian retail unit (GM1903) running OxygenOS 9.5.5
Enable USB debugging and OEM unlock in Developer options
adb reboot bootloader
fastboot oem unlock
fastboot flash system_a _your_gsi_path_
fastboot flash system_b _your_gsi_path_
fastboot --disable-verity --disable-verification flash vbmeta vbmeta.img (stock vbmeta.img extracted from official update package)
So after this i successfully booted into the rom, and everything including camera, bluetooth, NFC works out of the box.
There are only 3 bugs:
1. FingerPrint Scanner is not working.
2. VoLTE call works but it cannot be ended it gets stuck on "Hanging Up".
3. Ambient Display
Here you guys can find the download links:
Our Device a/b type so image must be arm64-ab.
I am also trying Lineage/Havoc/Pixel Exp and will publish the results here.
I tried almost every available rom available as generic image and all have only those 3 bugs mentioned above.