So if anybody wants a solution they won't have to scour the internet for what are essentially the same uses over and over again
Here's a short list I made through searching this sub and other threads+articles:
#WARNING: Keeping your phone constantly plugged into the charger for long periods of time may cause the battery to swell up and potentially explode
#WARNING: Keeping the screen on constantly on a phone with an OLED screen will likely cause burn-in eventually
Keep it as a backup phone
Dedicated camera
Dedicated music player (especially LG phones with qDAC)
Baby/pet monitor
Use it as a smart doorbell
Use it to record POVs akin to GoPros
Smart Home controller
Bedside alarm clock
Universal remote
Remote PC controller
Help science by lending your phones power for research
Dedicated eReader
Dedicated gaming machine
Webcam
Dedicated car phone for GPS etc
Dashcam
Digital photo frame
Education tool for kids
Video call device
Wifi extender/hotspot
Host a media server on it (Plex etc)
Host a normal server on it (c. /u/3Werve)
Timelapse camera
Give it to kids
PC Statistics (CPU, GPU usage)
Wireless adapter for wired controllers
Kitchen recipe guide
PC Monitor
Macro pad for PC
White noise machine
Disassemble and make an art piece out of it
Experimentation (e.g trying out apps or ROMs)
Dedicated chat device (Whatsapp, Telegram etc) (c. /u/utakatikmobil)
Cast Receiver (c. /u/Substantial_Berry_14)
m3u IPTV player (c. Substantial_Berry_14)
###No uses fit you?
Donate it
Recycle it
Sell it
I may link to examples or guides but for now im a bit too lazy. Googling should be enough, if not add site:reddit.com to the end of your query
I've considered using mine as a camera for a fixed install before, but the battery swelling thing is kinda scary. Doesn't help that a lot of modern phones don't seem to work without a battery installed, and that they often use ribbon connectors or other awkward setups internally. (so no just soldering a fixed power adapter to some pins)
Does anybody happen to know a software way of limiting charge to, say, 50%? I'm wondering if that'd help, as you'd at least be keeping the battery outside of the range where it's hardest to shove more power into it.
I wonder if you could have the charger plugged into a timer (like the kind you use for making lights go on and off when you're not home) so that it only charges long enough to keep it in the happy 20-80% zone? Surely some clever timing could make it work. Only keep it on long enough to charge up 60% (from 20 to 80), and have it off long enough that it drains down to 20%.
...that's a thought. Now I'm wondering if I could scavenge a smart power plug/strip somewhere and do a bit of programming to automate things that way. A project for later, maybe -- ended up picking up a few old webcams and they're doing the job so far.