Can I use 30W MacBook M1 charger to charge my iPhone 12 mini?

Apple says it is compatible.

30W USB‑C Power Adapter - Apple

If it’s 5volt dc there is no upper limit for watt

Watt  is like how fast your car can drive, but the speed limit is how fast your car do drive

the iphone draw as much current as it was build to use when charging, the fact that a charger can provide a lot more just means it's not having its full capacitive used

I did, if it output 5volt dc you can use any charger from 5watt to 5gigawatt

ohms law and all