I think part of the strain is as well as spending way too much time on screens (either slouched over staring down at a hand held or slouched over with head forward posture staring at a bigger monitor) is just spending too much time upright in general. Some work places are incorporating standing desks which seems to be a good thing but even still over a standard work day it's a really long time to be making those core muscles hold your body upright.

If we have to be at desks for that long, maybe we need more reclining workstations XD

On your point on not enough exercise, I have noticed the kids at our gymnastics club tend to stand and walk with good posture, and will even generally sit with good posture when chatting to people (although if sitting on the ground they may also casually adopt positions which most people would find uncomfortable XD) but that all goes out the window if they're hanging around by themselves or sharing screens, then they can slouch with the best of them XD