Should I make a reservation on a train from Munich to Zurich or just get a ticket and seat at the station. I want to be flexible because we are flying in to Munich and then heading to Zurich on the train. I’d like some wiggle room on which train to take in case my plane is late and customs takes a while
TIA
First of all, please note that the EC line Munich - Zurich is still interrupted until July 7th due to the catastrophic floods in Bavarian Swabia. If your travel date is during this period, your only option is to take regional trains via the alternative route Munich - Kempten - Immenstadt - Hergatz to Lindau and change there to the EC to Zurich. Or you could travel with Flixbus.
Otherwise, I don't think that all seats on the train will be completely sold out on your day of arrival, and even if they were, you would always find a seat on this train (outside the Oktoberfest period) because not all seats are bookable. However, the price of this flexibility is high, because a last minute ticket is at least 50% more expensive than a train-specific "Sparpreis" ticket.
I'd download the DB Navigator App and register, so that you can monitor the booking situation and book your train while waiting at the luggage belt instead of queuing at the busy DB counter in the airport
Travel Date July 18, would that be a problem?
If you want flexibility you need a "flexpreis" ticket, and that ticket is the same price, regardless wether you buy it in advance or on the spot. For the cross border EC service to Zurich tickets come automatically with a reservation.
Problem is that the route is more popular than the railways expected, and as a result sometimes there are no reservations available last moment. So book a flexible ticket for a departure you are fairly certain you'll make, and exchange the reservation at the station if you happen to be able to leave earlier.