Check out Hase bikes. They make several trikes with Shimano STEPS electric assist. We own a Hase Pino tandem which many folks use to accommodate different abilities. However, our Pino is not a trike. Their Lepus and Kettweisel trike models have Shimano STEPS versions.
Hase is a German company and finding a stocking dealer near you in the USA may be problematic. Their US distributor does promote Hase to the differently-abled community and can provide you with some assistance locating a dealer.
https://www.hasebikesusa.com/
With regard to other types of trikes, I've done a little bit of business with a dealer in Greenville, Tennessee who actively works with the VA to accommodate injured veterans. You might consider just giving them a call and see if they have any recommendations.
https://www.poweroncycling.com/
You mentioned looking at the Pfiff trike. Pfiff makes versions with the Bosch electric motor. I would highly encourage you to look for a trike with factory integration of the electric assist system. It won't be cheap, but a trike with Shimano STEPS or Bosch integration will have much better support than some of the less expensive Chinese hub motors. We own a ebike with a motor from the bankrupt and out of business Bionx. The Bionx motor works for now but parts and replacement battery packs will be a problem.