Android does not allow always on background processes.
Discussion
Other apps seem to have always-on background processes. BOINC is an example of a tool which does this. Syncthing seems to have this figured out.
They're probably just good at making it seem like that.
Android is very aggressive about killing processes every time the device's screen is off for more than a few seconds
Sure, but again, they have it figured out. BOINC for example, I know for certain is running in the background on one of my phones. I don't touch it for days or weeks and it's still computing and sending workunits back to the server. Zeus also has an always-on LND option though I've found it less reliable with this option enabled.
I guess those processes might be less intensive than a lightning node
BOINC absolutely isn't, it's an app that runs 100% of CPU 100% of the time.
Then it's not doing that on Android unless it has special permission from google or something
It has no special permissions. It's been out for many years, tens of thousands of people run it, it's OSS if somebody wants to use the code for a wallet.
If it has no special permissions then it doesn't run 100% CPU 100% of the time on an Android phone. Instead, the phone kills the process in sleep mode. This argument is pointless
I'm telling you that it literally does run at full CPU all the time, in the background, while the screen is off. That is literally the point of this application. I run this app on several Androids and my phone isn't a fluke, tens of thousands of people use BOINC to donate computational power to scientific research. I don't doubt that it difficult to this on Android, I'm just saying I have clear evidence that it's not impossible. Here's the combined computational power on a graph. https://www.boincstats.com/stats/-1/host/breakdown/os/0/0/1000
Or here's another app, that does the exact same thing, though I have less experience with it. https://play.google.com/store/apps/details?id=au.com.vodafone.dreamlabapp&hl=en_US
The only way it could do that is if it had special permission from Google, like the processes that keep the phone ready to ring for calls. We can go back and forth on this all day and Android will still not allow always on processes
I hate Google for this btw, or I'd try to be more helpful with finding info beyond just telling you my contradictory knowledge. Sorry