So the easiest is to just fly on an airline that doesn’t have Max planes. Like easyjet, frontier, wizz, Delta, British Air, and Air France are all airlines I know don’t have Max planes. I have heard some travel sites tell you the model of planes for a flight and may even let you sort by model. If nothing else you can look a plane up by its tail number. Often you will find that listed some were in the info about a flight.
So the easiest is to just fly on an airline that doesn’t have Max planes. Like easyjet, frontier, wizz, Delta, British Air, and Air France are all airlines I know don’t have Max planes. I have heard some travel sites tell you the model of planes for a flight and may even let you sort by model. If nothing else you can look a plane up by its tail number. Often you will find that listed some were in the info about a flight.