[OnePlus 7T Guides, News, & Discussion] Chxc:
Preparation:

Notes are important, please pay attention

ONLY use stock USB-A to USB-C cable

I have tried the stock cable from Axon 7, fail fail and more fail, don't make this mistake

DON'T store flash files on USB storage.

fastboot will timeout if your flash files are stored at a slow storage device such as a USB drive, or slow computer with eMMC drive

Download and extract the patched MSM download tool and related flash files (credit)

Download and extract TWRP 3.4.0-2 Test by mauronofrio (credit)

Download and extract 10.0.13-GLOBAL-OnePlus7TOxygen_14.O.19_OTA_019_all_2009281709_1026-FASTBOOT.zip (credit)

Optional: Unlock bootloader at this official OnePlus page with those steps

automated process you have to wait 1 whole week for

if you take this route, you will have an easier time get into EDL

Optional for Driver and boot into EDL: Download and extract the TOOL ALL IN ONE (credit) (untested) (can skip this step if you have driver and completed preparation step 7)

Flash Operations:

Run the MSM executable with Administrator Privilege

Boot into bootloader on 7T (if you already have adb connection, adb reboot bootloader would work as well)

Restart device: Vol Up + Power

Boot into recovery: when system reboot from step 4, immediately press and hold Vol Down + Power until recovery screen

Boot into fastboot: English -> Advanced -> fastboot

Boot into EDL on 7T

If you have OnePlus unlock token from Preparation step 7

Connect USB cable to both PC and 7T

on MSMDownloadTool, click Enum to display your device

fastboot flash cust-unlock unlock_token.bin

fastboot oem unlock

fastboot boot twrp.img

when TWRP boot: adb reboot edl

on MSMDownloadTool it will now show connected

If you don't want to wait for token (untested)

Use TOOL ALL IN ONE

Or, hold down the buttons then click start in MSM. If you release the volume buttons early it will kick you out of EDL--well at least for me. you can release the buttons once MSM starts (credit)

When MsmDownloadTool display connected, hit Start until 7T display CORRUPT message (normal behavior) and reboot into fastboot by ITSELF. If your 7T doesn't get into fastboot screen automatically, something is wrong with previous step, redo EDL flashing and do NOT proceed.

Start Power-Shell with Administrator Privilege and go to the extracted path of 10.0.13-global-oneplus7toxygen_14.o.19_ota_019_all_2009281709_1026-fastboot.zip (DO NOT USE DOS, it will fail you miserably)

Unlock bootloader: .\fastboot flashing unlock_critical (suggested, because it works, so I didn't test the oem unlock method)

To avoid potential conflict with installed fastboot binary (possibly lower version), you can either

edit the flash-all.bat, and change fastboot to .\fastboot, such that only the local fastboot binary will be invoked instead of pathed binary

OR run those identical commands with copy and paste

.\fastboot -w
.\fastboot flash boot boot.img
.\fastboot flash dtbo dtbo.img
.\fastboot flash modem modem.img
.\fastboot flash reserve reserve.img
.\fastboot flash recovery recovery.img
.\fastboot --disable-verity flash vbmeta vbmeta.img
.\fastboot --disable-verity flash vbmeta_system vbmeta_system.img
.\fastboot reboot fastboot
.\fastboot flash abl abl.img
.\fastboot flash aop aop.img
.\fastboot flash bluetooth bluetooth.img
.\fastboot flash cmnlib cmnlib.img
.\fastboot flash cmnlib64 cmnlib64.img
.\fastboot flash devcfg devcfg.img
.\fastboot flash dsp dsp.img
.\fastboot flash hyp hyp.img
.\fastboot flash imagefv imagefv.img
.\fastboot flash keymaster keymaster.img
.\fastboot flash LOGO LOGO.img
.\fastboot flash multiimgoem multiimgoem.img
.\fastboot flash odm odm.img
.\fastboot flash oem_stanvbk oem_stanvbk.img
.\fastboot flash opproduct opproduct.img
.\fastboot flash qupfw qupfw.img
.\fastboot flash storsec storsec.img
.\fastboot flash tz tz.img
.\fastboot flash uefisecapp uefisecapp.img
.\fastboot flash xbl xbl.img
.\fastboot flash xbl_config xbl_config.img
.\fastboot flash system system.img
.\fastboot flash vendor vendor.img
.\fastboot flash product product.img
.\fastboot reboot

Few notes

User data is wiped, again, lol

reserve partition flashing can produce error msg: FAILED (remote: '(reserve_a) No such partition'), it is OK but others should not Fail

Device will reboot once during the flashing process

After reboot, device will NOT go into fastboot screen but instead go into stock recovery screen, however fastboot will pick up and resume flashing the rest, ONLY IF YOU ARE UNDER POWER-SHELL, so DO NOT flash under DOS

if anything else fails besides the reserve partition, repeat step 7

Device will boot into system, you may use the OS updater to upgrade to the lastest firmware then relock bootloader or proceed with root with Magisk

Hope this will save you some precious time. Major kudos for previous contributions from post 1 and post 2.

All steps are recorded from memory, please let me know if any mistakes are in need of correction.

Tested working on Dec 5, 2020