I found my old Moto E4 (5th gen as some site says) not long ago.

Decided to wipe it so I can give it out and... things went south really hard because built-in wipe in LineageOS borks the OS loader and no amount of flashing works. In the end I even borked the boot loader and things started to look really awry. I found a way to flash it, thanks to the guys[0] who found a sploit for MTK loader - and confirming what E4 was one of the most 'unkillable' phones of it's time.

But the hardest part wasn't that but:

actually finding a working copy of the official firmware

Google Apps really-really-really wants to update it all to the most current versions... and then it's just starts to fail every 5 seconds with an annoying modal notification.

Thankfully, F-Droid was already installed so I just disabled everything Google and made a... not-so-dumb phone. But, despite it working good enough - it's totally useless for anything other than calling and e-mailing with a 3rd party client (would K9 even install on it? I don't know).

[0] https://github.com/MTK-bypass/bypass_utility

You could potentially use it as a security camera with some modifications or turn it in to a webcam. That phone probably has a better camera than 90% of laptops and cheap security cameras.