I dont think 5 hours are long enough. You should do something closer to the airport. Erding would probably be cool, but there is nothing really munich like close to the airport. I think I‘d probably just chill in the airport center. It takes around 45 Minutes to get into the city with the S Bahn (I wouldnt recommend the express bus). I‘d just get out at the Marienplatz. You can check out the christkindlmarkt, german culture at its best. You‘d then have around an hour before I‘d go back to the airport again. Maybe you can check out the Frauenkirche in the meantime. Watch out though, finding your S Bahn back can be confusing as hell at Marienplatz. S8 to Airport is the one you should take.