Help planning an ideal itinerary of 10 nights early August starting in Munich ending in Venice

Arriving in Munich. Departing from Venice. We will have 9 full days not including arrival or departure dates. Thank you

TL
With ten nights, I am assuming night one is arrival day, and day 11 (after night ten) is departure day. That makes 9 days for sightseeing. Munich deserves 4 full days (you can include Dachau with Munich if you want )....nights one through five. Day 6 travel to Venice and stay there nights 6 through 10. That is four full days in Venice. I don't think you have enough time for another stop without shortchanging Munich and Venice.
However, if you do want to add somewhere else, Vienna is a good choice. I really loved it when we were there!
Day one (night one) arrive Munich; days two and three Munich; day four travel to Vienna (night four); days five and six Vienna; day 7 travel to Venice (night seven); days 8 and 9 Venice. This leaves you with an extra day to add on to one of these locations. My choice would be Munich, then Vienna, last Venice. But that is just me. Have you checked into the flight situation to/from Munich and Venice? I am not familiar with the options you might have.
Whatever you decide, have a great trip!

Add Salzburg? Munich-Salzburg-Venice? Lauterbrunnen would fit the bill too but it's more train (although train rides can be nice too.)

Rick Steves at a glance key sites below for Munich-Salzburg-Venice. Happy travels!

https://www.ricksteves.com/europe/germany/munich

In the Center
▲▲ Marienplatz Munich's main square, at the heart of a lively pedestrian zone, watched over by New Town Hall and its glockenspiel.
▲▲ Viktualienmarkt Munich's "small-town" open-air market, great for a quick snack or meal.
▲▲ Hofbräuhaus World-famous beer hall, worth a visit even if you're not chugging.
▲▲ Residenz Elegant family palace of the Wittelsbachs, awash in Bavarian opulence. Complex includes the Residenz Museum (private apartments), Residenz Treasury (housing Wittelsbach family crowns and royal knickknacks), and the impressive, heavily restored Cuvilliés Theater.
▲▲ Alte Pinakothek Bavaria's best painting gallery, with a wonderful collection of European masters from the 14th through the 19th century.
▲▲ Lenbachhaus Three stages of German art: 19th century, Blue Rider, and post-WWI — most important for its Blue Rider collection.
▲▲ Nazi Documentation Center Thoughtful look at Munich's role in the rise of Nazism
Outside the City Center
▲▲▲ Dachau Concentration Camp Memorial Notorious Nazi camp on the outskirts of Munich, now a powerful museum and memorial.
▲▲ Nymphenburg Palace The Wittelsbachs' impressive summer palace, featuring a hunting lodge, coach museum, fine royal porcelain collection, and vast park.

https://www.ricksteves.com/europe/austria/salzburg
▲▲▲ Salzburg Town Walk Old Town's best sights in handy orientation walk (outlined in my guidebooks, and available as a free audio tour).
▲▲ Salzburg Cathedral Glorious, harmonious Baroque main church of Salzburg.
▲▲ Getreidegasse Picturesque old shopping lane with characteristic wrought-iron signs.
▲▲ Hohensalzburg Fortress Imposing mountaintop castle, with small museums, commanding views, and concerts most evenings.
▲▲ Salzburg Museum Best place for city history.
▲▲ Sound of Music Tour Bus or bike through S.O.M. sights of Salzburg and surrounding countryside.
▲▲ Mozart's Birthplace House where Mozart was born in 1756, featuring his instruments and other exhibits.
▲▲ Hellbrunn Palace Lavish palace on the outskirts of town featuring gardens with trick fountains.

https://www.ricksteves.com/europe/italy/venice
▲▲▲ St. Mark's Square Venice's grand main square.
▲▲▲ St. Mark's Basilica Cathedral with mosaics, saint's bones, treasury, museum, and viewpoint of square.
▲▲▲ Doge's Palace Art-splashed palace of former rulers, with prison accessible through Bridge of Sighs.
▲▲▲ Rialto Bridge Distinctive bridge spanning the Grand Canal, with a market nearby.
▲▲ Correr Museum Venetian history and art.
▲▲ Accademia Venice's top art museum.
▲▲ Peggy Guggenheim Collection Popular display of 20th-century art.
▲▲ Frari Church Franciscan church featuring Renaissance masters.
▲▲ Scuola San Rocco "Tintoretto's Sistine Chapel."