[G4 Q&A, Help & Troubleshooting] TeEmZe:
Well, I have essentially done everything wrong that you can do wrong.

For security considerations, I wanted to disable my baseband modem on my LG G4 H815 (currently having /e/ installed) - see this beautiful post for the instructions.

As I don't have root, I had the genius idea to do it all via the TWRP recovery. Once booted into the recovery, I had to enter my encryption lock, but that didn't work. I had yet another genius idea, thinking that I probably wouldn't have to unlock the encryption, as I only wanted to disable the modem (and didn't care to backup my data). So I entered TWRP leaving the system read-only.

Then I entered the terminal and wanted to disable the relevant services, as described in the post. However, the pm command wasn't available in the TWRP shell, so I had the genius idea to just skip those steps.

I then wanted to override the radio with zeros (as described in the post). However, the exact file from the post didn't exist, so I had the genius idea to overwrite /dev/block/platform/soc.0/f9824900.sdhci/by-name/modem instead. However, I firstly wanted to back it up to my external SD (I assumed that wouldn't be affected by the encryption) and did so with dd. After also having the modem overwritten with 0s (and synced) I rebooted to system, where I got the error that "Settings," stopped working and my phone started rebooting to recovery.

I thought "oh well, I'll just restore the backup modem from the SD", however I had to realize that (probably because I hadn't mounted the SD properly) the file didn't exist on the SD (anymore).

That's the current state. As I don't really want to lose my data (that I didn't backup), I haven't tried re-flashing anything yet (especially as I don't know if this'd help).

Is there any way to recover the "modem" without losing my data? Or, even better, is there a way to continue disabling the modem, with my phone properly booting again?

I really appreciate your help - please let me know if you need further information.

EDIT: It would probably be super helpful (and enough) if someone out there with the H815 could dump the content of their modem dev and share it with me. I don't think (?) that's included in a system image - at least it isn't mounted in system.

EDIT: Let me provide some instructions on how to (presumably) safe my day, if you have an H815 with TWRP recovery and adb on your computer:

Reboot to recovery:

adb reboot recovery

In TWRP, mount your Micro SD card or another partition you can read & write to (Mount -> Tick Micro SD card)

Restart adb:

adb kill-server

Enter adb shell:

adb shell

In adb shell, validate that your SD (or other partition) is correctly mounted (you should get the contents of your external SD):

ls /external_sd

In adb shell, dump data from modem and exit adb shell:

dd if=/dev/block/platform/soc.0/f9824900.sdhci/by-name/modem of=/external_sd/modem.img
sync
exit

Pull dump from device:

adb pull /external_sd/modem.img

Upload modem.img from your computer (from the directory you executed above command from) to some cloud

Share a link to the file with me

I'd be very grateful if someone could do this. Please feel free to ask questions about the procedure or to help me in any other way.