>> Will wrapping the electronics of my drone in copper foil make my drone impervious to this?

If it does, you will likely lose any GPS and remote operating capability you have.

Also, a high powered Maser might just burn through foil.

And weight is a big factor for drone design.

Copper isn’t lightweight

Aluminum or magnesium would do comparably fine. The shield can also be finely perforated to cut down more weight.

But you only need a super thin layer because it's so conductive. 0.5mm would be plenty.

Also, if this weapon is really powerful, you won't keep the frequencies it operates on a secret. Something able to fry a protected drone half a mile away is detectable on the other side of the earth.

And when the enemy knows what frequencies this operates on, they can use quarter wave chokes in the sliding electromagnetic seals around the propeller shafts etc, making the craft able to withstand even more microwave power.

Why would it operate on one strictly defined frequency? I would expect several quickly switched, and maybe even a chirp-style sliding frequency pulse, exactly to render narrow-band protections ineffectual.

because the only known way to make very high power microwave emitters, the magnetron, makes only a narrow band.

Makes sense. Add several with different resonance frequencies. This would also make the device degrade more gracefully if one of them dies.

If your drone had a way to communicate with the external world that would be its achilles heel. Im sure this is being researched as we speak and this type of defense weapon will make an impact on FPV warfare drones, maybe they will be designed in a new way to combat this or they’ll learn to detect what to stay away from.

adjustable attenuators are well known already. Software inside the drone can dial up the attenuation on the antenna whenever it is under attack.

Also, by using ultra wideband for the comms, there will always be some frequencies that an attack isn't happening on - and sets of notch filters can let those through.