Dual SIM is supported for Global ROM and EU ( I think, not sure) but definitely not Indian ROM.
I used USB 2.0 all across and haven't tried 3.0 . After Part 2 , i did not see Dual SIM enabled , I had to get the Global ROM as indicated below to actually see the Dual SIM.
ONE MORE THING
- I read somewhere that you need the Dual SIM Tray with two SIM cards in it when you are updating it to Global ROM to get the two IMEIs show up.
In Part 3 , step 4 I used this Downgrade ROM for Global from this thread
As OnePlus doesn't always provide download links for all of their OxygenOS ROMs & OTA update zips, we've created an index to put the links in one post so that they're easy to find. Note: This is not a support thread for issues you may have with...
The actual zip is
Check the attached screenshot.
Then I let the system update itself by going to the settings and checking for updates, i think the next upgrade enabled dual sim for me. I did this all the way to Android 13 and dual sim was retained.