See this thread about lightweight bikes.
https://electricbikereview.com/forums/threads/electric-road-bikes.26226/
Be wary of mid drives except yamaha if you intend to pedal. Ravi may have special knowledge about the shimano drive he mentions above, I hadn't heard that it had a one way clutch in it allowing the motor to rest while you pedal.
Yamaha mid drives and geared hub motors are the two kinds that don't drag when you pedal.
The magnum metro is 59 lb compared to the 44 of the yamaha you mentioned, but they might have some models that delete the rear book rack. there is 10 lb of battery on that model, 13 AH which should give some decent range. Magnum metro is geared hub 500 w. That is 19" seat post to handlebar stem, which is too big for me but may be right for you. Try some pedal bikes to see what size frame fits you.
I you are male and under 60 I expect you can work out up to lifting 60 lb on a bus.
I would not convert a carbon frame bike with a hub motor, they exert torque on the flanges. Aluminum is as low as I would go, and I would use torque arms in that circumstance to spread the force and cut the torque. The 53 lb bike left has an aluminum frame, converted with a 1000 w hub motor. the added 17.5 AH battery, battery frame, and DD motor brought it up to about 75 lb. I don't mind because i often carry 60 lb of supplies, which swamp the motor/battery weight. I pedal mostly to keep my heart/lungs in shape, limiting the electricity to times when the wind is >12 mph in my face or the trip exceeds 25 miles.