[OnePlus 10T 5G] beatbreakee:
So sorry for the delay... But yes your rollback package worked in getting me off the T-Mobile 2419 , and now I'm on the 2415. A.08 (yay . KINDA...)

Unfortunately this did not have the intended outcome. I mean yes the phone works properly and all... But I'm sure you knew that fastboot did not come back. (Wouldn't be that easy huh?).

Now, here's the next phase.... After repeatedly beating on OP via their chat, and yelling at person after person, I got one of them to slip up and let a few MINOR things leak verbally.

(Bear with me cuz I might be stating something that might be slightly off from him... I could tell English wasn't his 1st language... Or even 2nd)

"Sir what you are requesting is a file authorization to unlock the bootloader on your device, correct" --- OP

"No, because even if I HAD a special file, I would not be able to flash it, because I have NO fastboot mode accessible on my phone. YOU removed or disabled it yourselves!" ---- Me

"Ok after reviewing your previous words sent, I think I know what it is you seek. There is a program called MSM, do you know of, yes?"-OP

"YES I know exactly of that, and you guys made it password restricted so I cannot log in to get what I need, so is it possible you can refer me to get an access account for the tool?"-Me

"Unfortunately sir that is department not of ours, but I will forward your request to them for email response by 24hrs."-OP

"Ok... So what then, you or them will get back to me with info on how to get an account?" -Me

"Well it yes, sir I do not know if that is how they resolve, or maybe they just give you factory fastboot ROM which can be use with the updater application, for local flash. It is my knowledge that other devices we have sold have had this ROM load special fastboot to allow unlock/lock/flash/wipe commands to be sent from your PC, but it was special tool for devices that not have it already!" - OP ...

BINGO!!

I'll spare you the rest of the chat, but of course no one has contacted me....

SOOO... here's my thoughts...

1. This phone is like Samsung in that there is NOT a permanent bootloader lock, and instead there's just a custom ROM (like the old "Combination FW" that restores permissions for higher level functions aka 'Fastboot ROM"

2. This ROM could TECHNICALLY be created or the fastboot portion extracted from another one that already is out for one of these older devices, and we swap it into one of these rollback packages, cuz I did edit the payload properties file to test if simple changes can be made and it still flash... (Answer : yes... It worked!)

3. One of you GURUs who have found TEMP ROOT access on so many other 'unrootable' devices, discover a way in to these, in which we can access the partition where the bootloader exists, and turn it back on with a hex edit, or flip it to UNLOCKED, then I can use Qfil or an EDL prog to flash custom recovery!?!

The reason I say turn it back on is because I am fairly confident it is still functional, primarily because it shows for a half a second, then reboots back into normal mode if 'adb reboot bootloader' is used. How can it be GONE, If the OS still recognizes it. (This suggests there's a script or init command being triggered once that command is sent, and it forces reboot before fastboot can connect to your PC! ... There is still a splash screen triggered from the command... AND all the updates and rollback packages are using something other than EDL to flash all the partitions as .img files, cuz EDL can't communicate with a device while running, but those packages loaded via local update are prepped while running, and processed only by a reboot, which almost confirms that it's fastboot being used. Fastbootd will not process ANY img files, but it does recognize every reg fastboot command!

(Sorry again for long post but I figured detail is needed to solve this.)

I have 48 hours to completely brick this device and still return it, so I am up for ANY actions that you all might suggest, with no regrets! If I get it AT LEAST rooted, I'll take it! Or if we get fastboot enabled again even better. I will monitor this thread for your replies.

Thanks for all input!