Earlier quoted context omitted.
https://www.google.com/search?q=sitting+harmful+even+if+you+... Sitting for long periods tightens the hamstrings and cuts off circulation to your legs. Even if you exercise. Standing for long periods may give you varicose veins. Not sure there's a real solution here, other than to periodically disrupt any form of immobility.
The best posture is a varied one.
Or, it's like the idea doesn't have the magic of an idea that you can't do right now but won't require any effort when the time is right- like "I could get up every few minutes and stretch and walk around already! That can't be it... I need to buy a standing desk and that'll make me stand all day so I'm healthy."