Seriously how do you do this for any length of time? I would have neck and back ache and my hands would cramp up after just 1 day.

I did this for a bit during the pandemic (because my productivity approaches zero at home) unfortunately, it gets hot in the summer here, so working on a park bench in 110F heat isn't a year round option. I suspect there are few plaes in the US where this could work year round. I ended up just going back to the office--everyone else was gone, at home due to quarantine--and I could be very productive.