The squeal happens at very low speeds, right near the stop.
Off Line.. Go have live shop inspection.. Given Portland has a zillion bike shops.
make the rounds..
I have a bike with F/R SA drum hubs, no problems for 25 years..
this may be a not worn in, enough situation..
maybe add a Rim brake, lever, on the other handlebar..
it is not uncommon to have 2 brakes on the same wheel,
on tricycles