2021 400 boondock E brake magnet condition

Hard to tell from the pic, how much of a wedge shape does it have ? Clearly the part with the vertical lines has never touched the surface in the drum.

Wedge=how much is the left end worn down vs the right end which hasn't worn at all. When the magnet attaches to the drum it gets shoved backwards and wears more in the front (left side in the pic). If the brakes weren't used a lot and/or the brake controller is turned way down it it could cause little to no wear.

Ah, sorry it looks like the lever is on the left side in the pic. Seeing how little the magnet is worn there is no need to machine the drum. Check that the right side is actually working because seeing almost no wear is unusual.

Jack up the trailer with the battery turned on, pull the emergency brake cable out and try to spin the wheels.  If there is a difference in wear between sides, I would adjust the shoes.