I did it with the ROM from this thread:If you want to go back to OOS for me the fastest method is to use stock fastboot roms by Mauronofrio.If you need more help just ask.Another tip:if you are on Lineage then reboot to lineage recovery,wipe everything then from recovery reboot to fastboot,process is really straight forward
Things are changing with the advent of project treble and seamless updates. OnePlus will no longer release ROMs flashable via stock recovery (with twrp is possible but not recommended). The updates will be done on the slot not used for example...
I used the file: 10.3.6-OnePlus6Oxygen_22.J.48_OTA_048_all_2010042239_c0c1fee2
Meanwhile use TWRP Recovery for complete wipe, I restarted TWRP and got stuck in TWRP Recovery boot!
by CMD with ADB command I entered Flashboot and applied fastboot and everything ran perfectly !!!
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