I'm currently using an "old" mobile (Samsung A20) with Termux (standard ROM, not rooted) and works like a charm! I'm hosting the *arr suite, Kavita, Podgrab, Homeassistant, ntfy and there's still room left (in terms of CPU and RAM). In terms of consumption we're in the order of a few (<5W) Watts per day. The only issue is the storage, I've added a 128GB SD card and every once in a while I consolidate the content in an external HDD. And the nice thing is that you breath a new life in old hardware.