Can a microwave motor be powered by usb?
Microwave motors that I have seen are AC motors. There are very small motors with attached gears that might be suitable. They are sold for hobby and educational use.

Most of the power is lost in the motor and gear. The electrical input power will probably be more that twice the mechanical output power. A 5 volt USB supply may or may not be able to supply enough current. You will need to look at what is available. Sellers of inexpensive motors often don't supply clear information about the current required. Sometimes they just state free-running (no load) current and stall current. For a gear motor with the speed you need, the safe continuous current will probably be 2 or 3 times the no-load current.

If the load is too much for the motor, it will run slow, draw too much current and overheat. The stall current will be quite a bit higher. The power supply will need to supply the stall current for a fraction of a second when the motor is turned on. That could cause a "smart" power supply to switch off.