When you wake up do as many push-ups with good form in the morning as you can, then squats, and round it out with a morning walk. You can fine plans online for half marathons, I did one last year by myself and tracked it with my watch because the scheduled ones were stopped for CovId. Consistency is the key, do as much as you can without hurting yourself. In many places they have running clubs and groups so you can make it a group activity. At your desk you can find exercises to do, and do a few everything you compile or hit F5 etc.