[Galaxy Note 4 Q&A, Help & Troubleshooting] ren101099:
Thanks for the reply. Yeah, I think you're right when you say it was caused by uninstalling the Samsung DM service. I was worried that the problem was caused by dm-verity blocking the boot, but I read somewhere that dm-verity does not block boot until Android 7. Android 6 will warn about corruption, but will not block booting, if I understand correctly. So the bootup process apparently actually needs the Samsung DM service for whatever reason.

I ended up getting the phone working by flashing N910PVPU5DQI5_N910PSPT5DQI5_N910PVPU5DQI5_HOME.tar.md5 from 2017, which can be found here under "PREREQUISITE" as well as other places. I inspected the other, supposedly-2020 archive, and the only difference is the modem.bin is N910PVPU5DTI1 (supposedly from 2020) instead of N910PVPU5DQI5 (2017). I don't think I need the new modem, as I'm not using cell service, but if I want to, I think I can install it later with the stand-alone file "MODEM_N910PVPU5DTI1_REV00_CL_2079268.tar.md5" using the CP (modem) slot in Odin, if I understand correctly.

I think the CF Auto Root is not very good. I tried the Mobi .firmware site for an updated version, but I had the problem described here. So instead of CF Auto Root, I used the method described in the link below to root the phone, which involves TWRP and SuperSU:

https://xdaforums.com/t/simple-guid...ow-qualcomm-similar-for-other-models.3359832/

I had earlier found that guide in the Google search results for rooting, but as a newcomer I was turned away by technical jargon like "flash TWRP through Odin" that does not elucidate on what TWRP/Odin are or how to use them. But many days later, I now know what those words mean, and it is in fact very easy to "flash TWRP through Odin" once you know how to do it. (I think aspects of this website would work better as a wiki, so that people could add those details into the guide to improve it. The forums also have problems with information rot, like for example a link to release notes for SuperSU pointing to defunct Google+ (lol).)

Rooting it this way was much better, because when I soft-bricked my phone again by trying (again) to uninstall Samsumg DM Service with Titanium Backup (to confirm that that was what had caused the soft brick the first time), I was able to easily restore the system partition I had earlier backed up to SD card with TWRP. Doing it with TWRP backup/restore avoids the need to re-flash the stock firmware through Odin, and it also leaves installed apps (Titanium Backup, etc.) and data intact. If I had TWRP the first time I think I could have recovered that PNG image of my password from the filesystem and avoided orphaning a brand new Google account (but Google kindly allowed me to create another one). The stock recovery is really useless. The so-called "factory reset" didn't do anything for me.

The only other thing I could do is maybe install Magisk, but I'm not sure I really need Magisk — I just want to be able to run apps that require root, and I think SuperSU will be good enough for that. And the guide for installing Magisk goes over my head lol...

"if your device utilizes the A/B partition scheme" = I don't know

"If your device doesn’t have a boot ramdisk" = I don't know

So I think I will maybe avoid Magisk unless I find an easier-to-follow guide that is specifically written for my exact phone model.

Other than that, I just need to shut off the annoying Hands Free Activation that starts every time I reboot the phone. I will try to freeze the Samsung DM Service as you suggested, although it seems strange that that would work, because it seem like it would stop it from being available during boot in the same way that uninstall does. But I will try it. Now that I have TWRP and Odin and the stock firmware, I know that I can unbrick the phone if something goes wrong; I think it is unlikely to be permabricked, so I can safely experiment with more possible methods to shut down the Hand Free Activation 👍. I think Titanium Backup requires the premium version for freezing, but I might be able to do the same thing for free with Island or Greenify or some other app.

So yeah, I'll try to freezing it. In the meantime, if anyone has any other ideas about how to stop the "Hands Free Activation" / Samsung DM Service from running after every boot, feel free to reply...