Microwave NEC Codes
If the microwave is built-in, then a dedicated circuit is required for the microwave.
A countertop microwave can be plugged into one of the small appliance branch circuits.
Disclaimer: These codes are based on the NEC (National Electrical Code) 2023 edition and are provided for general reference. Local jurisdictions may have additional requirements. Always consult a licensed electrician and your local building department.