Can you watch Netflix on a mini projector?
Yes, although it depends on the projector and the method of doing so. Some smart projectors run on Android or have decent firmware and interfaces that allow apps like Netflix to be loaded natively on the projector itself.
Others require you to pair with a Netflix supported device like a smartphone via Bluetooth or Wi-Fi, and then screen share to the projector. This is basically streaming via your home (or work) network.
Other mini projectors support HDMI and MHL, and you may be able to watch Netflix on the projector via its connection to a smart TV, games console, PC, smartphone, or tablet.