The 737s are the most common airliner in the world, more than 10000 have been built, and more than 1000 are in the air right now. The pre-MAX 737s are just fine (though it had some issues with the rudder in the 90s, and, well, nearly 2% of all 737s built have been lost (184 hull losses) with nearly 5000 fatalities. Goes to show how much they fly.)