I have recently switched to Fairphone 5 and I am quite happy with it. One issue I have recognised is that the “Battery protect” setting to charge the battery at most to 80% does not work when charging while the phone is switched off. Is this a bug or a feature?
Welcome to the forum.
I’d say probably neither. Just that the code that manages the restriction requires the OS to be running. When the phone is off then you’re literally back to basics.
My own approach is to leave the phone running when charging (in fact I rarely turn it off nowadays, just enable Aeroplane mode at night if you don’t want to be disturbed).
the battery protect is a software feature, that OS can’t enforce when the phone’s shut down. same how, for example, it won’t start the alarm clock when it’s powered off.