Apple USB-C 20W Power Adapter
Can you use the Apple 20W charger for iPhone 12 pro with an adapter to charge an iPad Mini 3?
iPad mini 3 Wi-Fi, Cellular
Yes.
No problems or issues.
It doesn't matter what Apple power/charging adapter block to use as any Apple iOS device will use ONLY the power it needs from the power/charging adapter and no more.
Best of Luck to You!