I would also be really interested in knowing how to get the second SIM to read on the T-Mobile IN2017 variant of this phone. I've been tearing my hair out trying to get this to work, now that I've seen that the international models running Android 11 OB2 seem to have functional dual SIM. Personally, I kind of gave up on getting Android 10 to do dual SIM- even with the European ROM (which I'm fairly certain is the only way dual SIM on this device was ever officially supported by OnePlus), I haven't gotten it, but I think I'm annoyingly close. T-Mobile MSM to Global 10.5.12 to Android 11 DP2 will get you non-functional dual SIM- the device will see both SIM cards, and will properly identify them and their phone numbers, but the second SIM won't connect to voice or data, no matter what I do. If I upgrade the device from DP2 to OB2, the dual SIM UI stays (if I go directly from Global to OB2, it doesn't show), but the second SIM slot is still non-functional- no service for voice or data on the second SIM.
For anyone who has gotten a T-Mobile OP8 to properly read two SIM cards, I'd really like to know how- through my hours of messing around with this thing, it always seems like one step forward and two steps back. Hopefully the final release of Android 11 clears this up.
(My two SIMs are from T-Mobile and AT&T, respectively. Unfortunately, I don't think two T-Mobile SIMs has a chance of ever working with this setup on any firmware- "SIM 1" and "SIM 2" share an IMEI. While that's probably okay for SIMs from different carriers, that's not going to fly on the same carrier- it will look like a cloned IMEI to the network, and probably get shut down fairly quickly.)
