[OnePlus 7 Pro Questions & Answers] sidusnare:
TLDR: Yes I updated Oxy to the latest, yes I ran copy-partitions, yes the SIM is unlocked, yes it's boot unlocked, still can't get LineageOS 18.1 to see the SIM.

So, I got a couple T-Mobile OnePlus 7 Pros cheap off eBay. They came with Android 10.

I've got a Gentoo workstation that I do my primary work on, and an Ubuntu workstation, as well as a Windows 10 gaming desktop and laptop.

I had seen some things about the SIM and how you had to follow the instructions, so I do.

I check that the SIM is unlocked. I get this reassuring message that the SIM is permanently unlocked. It sees my SIM.

I upgrade to the latest update available from OnePlus, it's Android 11.

I check that the SIM is unlocked. I get this reassuring message that the SIM is permanently unlocked. It sees my SIM.

I enable OEM unlock

I boot into fastboot and flash lineage-18.1-20210620-recovery-guacamole.img

I boot into recovery

I run copy-partitions-20210323_1922.zip as instructed.

I install lineage-18.1-20210620-nightly-guacamole-signed.zip, MindTheGapps-11.0.0-arm64-20210412_124247.zip, and Magisk-v23.0.zip .

I boot into lineage-18.1

No SIM. I do a lot of things that don't make any difference at this point, but it looks like it sees a SIM, but won't accept it. Like, the Network Cell Info lists Operator as T-Mobile when I have my SIM in, and not when I don't which is correct because it's a T-Mobile SIM, but strange because the system UI won't even admit there is a card, but the system surelly knows there is a card.

So, I'm getting frustrated, and figure, alright, let's see OxygenOS use this SIM again, make sure it didn't just up and die while I flashed LineageOS.

Fastboot, check the active slot, set the other slot, reboot into recovery, nuke user data, boot the OS.

And OxygenOS boots up. It sees the SIM. I'm online... With Android 10... WFT? copy-partitions-20210323_1922.zip copied Android 10 over my nice freshly upgraded Android 11...

So, I had bought two, I go slower and more carefully with the second one.

Boot it up, Android 10, per expectations.

Check the SIM is unlocked, it gives me the nice unlocked permanently message.

I go to unlock the bootloader, and it isn't just doing it, it want's a code from 1+, so I do that whole wait a week thing.

Acquired and flashed the boot unlock and booted it into TWRP.

I imaged the flash, each partition by name, so I have a raw partition by partition image of the phone.

I boot it back up and let it update itself to Android 11.

Check the SIM is unlocked, it gives me the nice unlocked permanently message.

I booted TWRP and imaged it again.

I boot to fastboot and flash lineage-18.1-20210627-recovery-guacamole.img

I boot into Lineage Recovery.

I check the active slot, enable ADB, and DD the active (Android 11) over the inactive (Android 10).

Fastboot, change active

Boot into OnxygenOS Android 11

SIM is happy.

Fastboot, change active back.

Boot into OnxygenOS Android 11

SIM is happy.

I have now manually verified that both slots are the latest Android 11

I let copy-partitions-20210323_1922.zip run just in case there is some extra voodoo it does.

I install lineage-18.1-20210627-nightly-guacamole-signed.zip MindTheGapps-11.0.0-arm64-20210412_124247.zip and Magisk-v23.0.zip .

Format userdata

reboot

LineageOS 18.1... Still no SIM.

After this I do a lot of things, nothing productive, for example:

I extracted com.tmobile.rsusrv, com.tmobile.rsuapp, and com.tmobile.rsuadapter.qualcomm from OxygenOS and install it on LineageOS. After I manually add the permissions to get it to run, it crashes without anything helpful in logcat.

I tried to use MsmDownloadTool to install the "International Version" of T-Mobile's OxygenOS, but nothing I can do will get the phone to show up in the tool, and it's windows, so it's just impossible to actually work on, no way to tell why it won't see the phone.

I tried to use Qualcomm's qdl to install the "International Version" of T-Mobile's OxygenOS, but it won't recognize guacamole_21.O.09_190516.ops as a valid file, and I don't know enough about the format of that file to try to adjust the qdl code to make it flash it anyway.