Managers 100% lose their abilities, their focus shifts to completely different concerns -- codebase health, enabling people, tracking velocity metrics, etc. They still understand high-level concerns, of course (if we are talking about strong technical background), but they'd struggle a lot if just dropped into the codebase.

Tech leads can exist in many variants, but usually they spend the majority of time in code, so they don't lose it. If they become too good at managing and change their priorities, they _will_ gradually drift away too.