(SOLVED) you will need an EDL deep flash cable and some basic tech skills and know how, My oneplus 8t had gone dead after I carelessly flashed the wrong XML img to my phone meant for a variant with different ram. I had seriously thought my phone was super bricked. I tried everything from letting it sit until the battery would normally be dead and then charging for a 12-14hr cycle, and then turning back on with every button combination for every conceivable time intervals possible , both plugged into and unplugged (computer & wall charger). I even made myself an EDL deep flash cable and tried combinations with that. Nothing worked and I was close to writing it off, but then I thought, most phones have test pins for EDL mode, if the deep flash cable doesn't work. Heres what I did. Take a heat gun and heat the back of the phone around the outside to soften adhesive, take a card or thin plastic object and carefully pry off the back. You will want to remove the camera modules with has 4-5 tabs to the board, this will expose the two EDL test pins. Before shorting them out, disconnect the battery and more importantly, HOLD DOWN POWER BUTTON FOR AT LEAST 30 SECONDS TO DRAIN ALL POWER! Then reconnect the battery and immediately short the pins for at least 10-15sec. Then connect EDL cable first to your phone, then while holding the button on the cable, connect to PC. You should have the MSMTOOL ready and waiting for device at this point. If the phone is not acknowledged as connected by p.c at this point, LEAVE IT CONNECTED, and vol+, vol- and power at the same time for 10-15 seconds. This is what saved my phone, I hope that it helps to save yours as well..