There is no impact at all, slow charging is usually the best way to maintain battery life, fast charging will shorten battery life. The iPhone12 slow charge does not cause any damage to the battery, and unhealthy use will cause battery damage, including:
① Non-original charger,
② Using mobile phones at high temperatures, ③ charging while playing, the above three points are still relatively large damage to mobile phone batteries
The slow charging of the iphone12 has no effect on the phone, only the charging time is extended.