Unfortunately, especially with lower budget, that often ends up being choice between hardware and software.

I didn't want to run custom ROM on the X3 Pro due to warranty. I had the motherboard replaced thrice, on average surviving for 9 months each... But there were theoretically options.

Armor 24 doesn't seem to have any custom ROMs available, as seems to be usual with MTK devices, but the hardware is quite unique. I already had numerous strangers ask me what that phone is, how often it needs to be charged, or "what can that thing do" and "I am not surprised it has such strong light anymore" (it's a massive 85.14Wh brick).
To be honest I like how it feels in hand compared to a fragile thin slab.

But the only ones making crazy devices like this seem to be brands like Ulefone, Oukitel and Unihertz (they even have a projector phone like Samsung did, but modern) which most likely won't see custom ROMs, and I am too dumb to try building and maintaining something myself. I don't even know how it works with device-specific drivers.

I did, as I said, by returning the phone xD

I think I also (unsuccessfully) tried ADB.

Not a carrier phone. I don't know what specifically it is, Google Play... something. I disabled automatic updates in Play store, so probably something else. I usually just quickly pull down notification shade and click "Cancel".

Even disabling all available restriction settings often doesn't quite work. For clock app I set it to unrestricted and disabled optimization in DuraSpeed, still, it's a dice roll. The chances are lower when charging. (Ulefone Armor 24)
On previous phone Unrestricted setting and locking in recent apps also didn't quite work, but that phone had more issues. I'd often find that everything just randomly crashed overnight. (Poco X3 Pro)

But it also seems per-app. From experience, the most kill-resistant app is Termux (terminal emulator), but only if you disable child process restriction in developer settings. LibreTorrent also survives well, making the 2 only reliable large background download methods LibreTorrent and wget in Termux.

But anyway, my Alcatel 1066G dumb phone was just 10 bucks. A more reliable solution (and it supports animated GIF wallpapers 🙂).

Nothing about the app is secret, Google openly advertises it

Phew, I'm always terrified of that. It won't affect my gore folders, will it?

Lol, I think they asked for a firewall, not alternative OS