What can it compatible with? Can it compatible with other system device?

The keyboard and mouse set is compatible with macOs 11.3 or later ( For Mac mini /Mac Pro/ MacBook, MacBook Air/ Pro, iMac, iMac Pro, Mac Pro/Mini, etc). Could not fully compatible with other device and system.

Can I adjust the mouse DPI?

DPI 800-1200-1600-2400, you are able to change the DPI according to your different demands.

Is it have dual interface? Can it work with device that has USB port?

Yes, this 2 in 1 interface wired keyboard could compatible with USB and Type c port device ( NOTE: If you used the USB A interface, please make sure the Type-C is plugged into the USB A port.). The mouse compatible with USB A port only

How to connect the mouse? Does it have C interface?

No, the mouse only has USB A interface, but the keyboard has a USB A hub at the top for mouse connection.