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.

How big is the keyboard? Can it be put in a backpack for easy carrying?

Our keyboard: 11.22 * 4.72 inches ( keyboard+mouse weighs: 0.88 lbs )

Air 13 inch: 11.97 * ‎8.47 inches ( weighs 2.71 lbs )

It’s smaller and lighter than air 13-inch, ultra-portable and easy to slip into a backpack, perfect for daily use and travel

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.

Can I adjust the mouse DPI?

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