We would like suggestions on a place to stop for 2-3 days between Strasbourg and Salzburg in August. Bregenz looks interesting, but is it terribly crowded in early August? Are there other less crowded towns around Lake Constance we should consider? We looked at Augsburg but there doesn’t seem to be much to do for 2-3 days. We need easy access to the train.

https://bregenzerfestspiele.com/en/tickets/schedule?
The direct rrain line from Strasbourg to Salzburg goes via Karsuhe - Stuttgart - Ulm - Augsburg - Munich.
Lake constance is not along that itinerary, but its a area where you can easily spend 3 days.
Check:
Schaffhausen, Rhine Falls and Munot castle
Stein am Rhein
Arenenberg castle
Konstanz and Mainau Island
Unteruhldingen Lake dwelllings
Meersburg castle
Zeppelin Museum at Friedrichshafen
St. Gallen and it's world heriitage monastery
Lindau Island
Rhine river boat Schaffhausen - Stein am Rhein - Reichenau Island - Konstanz
Lake Constance ferries
Konstanz - Mainau Island - Unteruhldingen - Ueberlingen
Konstanz - Meersburg - Friedrichshafen - Lindau - Bregenz
Konstanz - Romanshorn - Rorschach - Lindau
Romanshorn - Friedrichshafen

There are 5 differentr itineraries from Strasbourg to Lake Constance:
Strasbourg - Karlsruhe - Stuttgart - Ulm - Ravensburg - Friedrichshafen - Llindau - Bregenz
Strasbourg - Offenburg - Gengenbach - Triberg - Donaueschingen - Singen - Konstanz
Strasbourg - Offenburg - Freiburg - Hoellental - Himmelreich - Titisee - Donaueschingen - Singen - Konstanz
Strasbourg - Basel - Schaffhausen - Singen - Konstanz
Strasbourg - Basel - Zurich - Bregenz - Lindau

Thanks, neckervd! I know there’s tons to do around Lake Constance, I’m thinking Bregenz will be crowded in August with the music festival? Is there another less crowded town you could recommend? What do you think about a few days in Augsburg? Or another charming town I might not know about?

Bregenz will not really be crowded because of the Bregenzer Festspiele as there will be played every day the same opera (Der Freischuetz), A lot of people go back to there homes after the performance, up to Zurich and Bludenz. Others will stay there just for 1 night.
All other towns around the lake will be as usual in summer: some German families in holidays allong the German shore and very few tourists along the Swiss shore.
Many day trippers from the towns between Stuttgart and Zurich, above all on weekends if the weather is fine,