[OnePlus 7 Pro Questions & Answers] HippoMan:
I have an OP 7Pro (GM1917) that was working fine for a long time with OOS 10.3.8.

I hadn't done an upgrade for a long time, and so recently, I did an upgrade to OOS 11.0.5.1.GM21AA. After doing that, my device is unusable, and I fear that there might be something broken or damaged that causes firmware or storage to no longer function properly. All of the explanatory details follow, and please read all of that. What I'm wondering is whether the device is now permanently hosed, or perhaps if there is some way for me to fix it. Here are all of the details:

After the upgrade, my device went into a permanent boot loop when trying to boot to System.

I then did fastboot boot twrp-3.6.0_11-0-guacamole.img, and it indeed put me into TWRP. However, the /data partition is inaccessible. Whenever I try to format /data, I consistently get these messages:

Failed to mount /data (Invalid argument)
Unable to recreate /data/media folder.
Unable to mount storage
Unable to mount /data/media/TWRP/.twrps
Unable to wipe data

I go back to the bootloader and connect to my PC, and I then run these commands:

fastboot erase userdata
fastboot format:ext4 userdata

These commands successfully run with no error messages. I then go back into TWRP, but /data is still inaccessible, and I get the same error messages that I listed above when trying to format /data .

I then tried to decrypt /data, but when I do so, it asks for a password, and I have no idea what password to give. I never used any password on the device in the past. I am not allowed to decrypt /data without a password.

So, I decided to use the MsmDownloadTool to reflash my device back to OOS 10.3.8. This works fine with a different GM1917 device that I have (but which I never tried flashing to OOS 11). However, with this particular device, after going into EDL mode, I am told that I am "Connected", but a couple seconds later it gives me the "Sahara Connection Failed" message. I have double-, triple-, and quadruple-checked the device drivers, and it indeed is showing that the "Qualcomm qds 9008" driver is properly installed and active. Furthermore, as I mentioned, I have no problem using MsmDownloadTool on that PC with another GM1917 device.

I went further: I extracted payload.bin from the OOS 11.0.5.1.GM21AA installation bundle, and I extracted all of the *.img files. I flashed boot.img via fastboot and retried everything that I mentioned above, but nothing has changed.

I then went and flashed all of the *.img files. However, still nothing has changed.

When reflashing the set of all *.img files, in some cases, I was told that the file is critical and cannot be reflashed. I then ran these two commands ...

fastboot flashing unlock
fastboot flashing unlock_critical

... but in both cases, I was told that the device is already unlocked. Trying to reflash all of the *.img files again gave me the same results: i.e., some got flashed, and others were not flashed due to being "Critical".

Also, some of the items I flashed were said to be "sparse" and their flashes were flagged with warnings, but as far as I can tell, they seem to have been flashed anyway.

Do these problems with /data and EDL and everything else mean that my device is somehow permanently damaged? Or are there perhaps one or more additional things that I can try in order to restore it to some sort of working state?

Thank you in advance for any thoughts or ideas.