The current thinking by Apple in iOS 13 seems to be that when the phone (or iPad) is charged to around 80% on a normal charge, the last 20% should be a slow charge, and I believe the software can control this.
This is the reason I always use a wireless charger for my iPhone XR, as itâs a slower way to charge, and although Iâm no expert, if Apple adopt it then so will I.