Munich to Zurich in 8 days

You say you have a conference and you have 8 days, but how long is the conference?
Or, how many days do you really have to get from Munich at the end of the conference
to Zurich?

Salzburg is 2 hours by train from Munich. Zermatt is 4 hours by train by Zurich.
Garmisch and St Anton are more or less on the way from Munich to Zurich. I'd
say that as long you don't try to hit 3 or 4 places and have 4 or 5 days, you could
hit any of those places. It's not that much of a extension or a backtrack. Innsbruck
is an option also. Hallstadt, as overhyped as it is, is about 90 more minutes from
Salzburg.

Are you open to renting a car and driving, or are you wed to trains?

How many days will you be at the conference? Maybe husband and kids can do Salzburg while you slave away at your conference.

Sorry I should have said . . . after the conference I have 8 days to travel . . . 8 days to see/do before needing to be on my flight out of Zurich.

I am open to trains or car . . . what do you recommend in that region? AND what are in your opinion the not to be missed places . . . do any of them require a car?

Public xport is very good in that part of the world, but you have to be open to
figuring out how it works, especially (IMO) if you start wanting/needing to use
buses as opposed to trains.

I will say that if you rent a car in Germany and return it in Switzerland, you'll most
likely pay a possibly large dropoff charge. But with 8 days, you could do 2 places
pretty well, and not really have to go in a straight line to Zurich to do it.

If you have a free half day while in Munich, there is Dachau. I would definitely
consider Salzburg; the festival will just have ended and perhaps it won't be quite
so crowded. If you want mountains there are multiple options; Kitzbuhel, Zugspitze,
Wengen/Murren, Zermatt. Lucerne is worth a day or two.

I am not answering your "best bets" question because that's kind of in the eye of the
beholder, and to be honest, your list of preferences didn't really narrow it down all
that much. But you have a decent amount of time. I might go with one city (Salzburg)
and then one mountain town/village to get some variety.

If you rented a car in Germany, and dropped it in Switzerland , you would get hit with a big International drop charge, The car would have to be transported back to Germany, and you pay for that and then some.

If you’re interested in art history, you could choose a relatively direct route and split your time between Oberschwaben (the Upper Swabian Baroque Route: https://www.oberschwaben-tourismus.de/en/world-of-travel/upper-swabian-baroque-route#/article) and Lake Constance; if you have a rental car, something like this:

(1) Ulm (gothic cathedral, fishermen’s quarter) and Wiblingen (Baroque monastery library)

(2) Zwiefalten (Roccoco church) and Ochsenhausen (with the famous Gabler organ)

(3) Bad Schussenried (monastery library) and Weingarten (Germany’s largest Baroque basilica)

(4) Ravensburg (medieval town) and Meersburg (beautifully situated on and overlooking Lake Constance; excellent state winery with a tasting room and a magnificent viewing terrace)

(5) Konstanz and Mainau Island

(6) Birnau and Salem

(7) Lindau and Bregenz - from the Pfänder (accessible by cable car), there is a great view of the lake

Accommodations in Upper Swabia can be found on short notice through Booking etc. or local tourist offices; I'd look in one of the small spa towns, like Bad Wurzach or Bad Waldsee. At Lake Constance, it’s advisable to book in advance (my favorite location is Oberreitnau, north of Lindau, but there are, of course, many other options).

In this particular case, I would rent the car from Hertz and return it in Lindau, because the drop-off fee in Switzerland would be very high. Hertz has a location about 300 meters from the Lindau-Reutin train station, where the train to Zurich stops. The other rental companies are farther away, so you would have to arrange your own transportation to the station.