Is it okay to leave my MacBook Air plugged in all the time?

Yes, it’s designed to handle it. Modern MacBook Airs (2018 and later) use Optimized Battery Charging to hold the charge at 80% until you usually unplug, so leaving it plugged in at 100% all day isn’t a problem. The real enemy is heat and leaving the battery at full voltage for months, but built-in battery management is good enough for most people. If you want to be extra careful, use a tool like Aldente to cap charge at 80%, but for typical users the difference is negligible.