[SOLVED] Is this motherboard compatible with ryzen 5 3600

It's a decent motherboard, however, it may need a BIOS update in order to support the Ryzen 5 3600, and in order to do this update, you will need an older CPU.

I would suggest one of the following board which will not need a BIOS update:
MSI B450 Tomahawk MAX
MSI B450 Gaming Plus MAX
MSI B450 A PRO MAX (not the B450m A PRO MAX)
 
That asrock above and all of MSI's -MAX motherboards are about the only B450s that can support Ryzen 3000 without potentially needing a BIOS update.

Leaving the extra 4 pins unpopulated is fine. There won't be any damage. The 8 pin alone can deliver like 300+ watts iirc, and no current Ryzen CPU will draw that.