fastboot flashing unlock_critical
[...] Getting into EDL mode took me a while because I'd never had to do that on any previous phone way back when I used custom ROMs. Note that in EDL mode the screen is blank, and apparently it times out after 10 seconds. So the way to do it is to power off the phone and disconnect the USB if it's connected. Then press both volume UP and DOWN at same time, then while holding those buttons down, insert the USB which should already be connected to your computer. The best way would be to have the MSM program already open on your PC, then put phone into ELD mode. I had my left hand holding the volume buttons on the phone (press hard with two fingers to be sure), used right hand to plug in USB, then right hand on the mouse to work MSM. Once the USB is plugged in, watch the MSM window and look for it to say "Connected". Then just click the Start button. You can then release the volume buttons on the phone and let MSM do its thing. [...]
fastboot oem lock
Tested, 100% working.
No risks, if there is an error you can just flash the stock TMO msm and you'll be 100% stock and working.
This is to bypass the need to sim unlock and to bypass the wait period of OnePlus. But this does not sim unlock the phone.
Did you reopen another cmd to do this? When I restart my phone into fastboot, Powershell continued to do its thing until my phone restarted and it got stuck.
I'll have to find another computer to try if that's not the case
I'm not sure. In my case, I had a driver that appeared to be correct but the MSM tool would just hang. If you have the phone running in edl mode you could check the driver version in device manager but I'm not sure how to verify which one is the correct one.
This is the driver I ended up using.