I would say there is a gap in the market for folding bikes with a wide gear range
the cheep way would be to graft Shimano Megarange parts onto a 21 speed 20 inch folding bike
>shimano RD-TX51 GS>shimano megarange tz31 - 14-34T-7+ an hub motor that works with freewheel and ur away
https://goldenmotor.bike/product/black-pie-5-vector-20-inch-rear-conversion-kit/or if the bike has a Freehub
>shimano RD m340>shimano hg31-8 34https://goldenmotor.bike/product/magic-pie-edge-vector-20-inch-rear-conversion-kit-8-10-cassette/ 