I want to disable iphone screen activation when plugging in a charger
There is no native way to achieve this. Here are some alternatives:

1. Low-light mode. Go to Settings - General - Accessibility - Zoom - Zoom Filter - Low Light. Enable zoom, double-tap the screen with three fingers, and you now have extra low light mode.

2. Buy a solar charger with a built-in battery

3. Jailbreak. There are many tweaks on this, but I will not list them here as I advise against jailbreaking.