Take your work meetings on a pair of headphones while dialing in, instead of video conferencing in.

Take a fifteen walk once a day while sorting out your daily schedule, working on a hard problem, etc.

Personally, that cooped up feeling from being stuck inside all day is one of the reasons why I moved out of the city and onto some property. 30m of daily outside chores (work breaks, lunch breaks, replacement for a "commute") and I easily get 10k steps a day.