Voici le pas à pas que j'ai écrit moi-même pour eux au cas où ils en auraient besoin.
So for those who get their OP8T bricked for some reason (bootloop, stuck on OnePlus logo, Qualcomm CrashDump Mode, etc), and tried everything without success AND bought it after March 2021 (I don't know the exact date, feel free to correct me), here are the steps to unbrick successfully your device and preserve your mental health.
1- Go to this download page and download this specific MSMTool for OP8T :
2- Extract files wherever you want in PC and open MSMTool as administrator
3- Select "others" in "user type" and click next
4- In "target" choose "H2" option and then click start
5- Power off your OP8T. If in EDL mode (black screen and no response) press Vol+ and Vol- and power button simultaneously during 10 seconds to exit the mode and boot in Fastboot mode and choose "Power off" option to shut it down.
6- Let the phone cool down for 1 minute and go into EDL mode by pressing both volume button WITHOUT pressing power button, and then connect the device holding the buttons to PC using official cable. The tool should shows "connected" in one of the COM slots, when the process start release volume buttons . If not showing "connected" then install/upgrade OnePlus and Qualcomm drivers before trying again.
7- Let the process going until the end, the phone will boot by itself in Hydrogen OS.
8- Choose "English" and skip all the welcome setup
9- Once in home screen, download the Oxygen OTA from this link :
10- Once the OTA package downloaded, put the file into phone storage and go to local upgrade from "Update" menu in Settings and flash it.
11- Let the process finish and the phone should boot directly in Oxygen OS ROM
Congratulations, you saved your OP8T from death and retuning it back to OP repair store.
The explanation for this, is that new OnePlus 8T's since March 2021 for some reason are all coming now with LPDDR5 instead of old LPDDR4, and the current MSMTool's are only compatible with "old" OP8T with LPDDR4. That's why flashing new OP8T with latest March 2021 MSMTool will bring you directly to Qualcomm CrashDump Mode.