I'm in a similar situation-- I'm 6'2" and just picked up a used RadCity 5 Plus Step-Through. I max out the seatpost and still can't get a full pedal stroke. It appears the stock seatpost is 27.2x400mm so I just ordered a cheap 27.2x450mm replacement post to see if an extra 5 centimeters does the job. I know a lot of folks are into the suspension posts, but the wide tires already make the bike feel cushy enough for me so I went with a rigid post. Plus it was $23.

Here's the link if anyone else looking: https://amzn.to/3xiVeEC

Love the inspiration here. I did mine with a hose clamp and it works great.