Lake Biel

If you have a car, on a clear day the view from Chasseral, right above the lake, is hard to beat!
The vineyards above Ligerz (accessed on foot or via funicular) are quite pretty as well - though not as much as Lavaux.
Other than that... I do not know, only ever passed thru the area.

Biel has a small beautiful old town. Plus, there are pretty little towns on lake Biel or on the nearby lake Neuchâtel like Erlach, La Neuveville, Twann, Le Landeron. For nature, you could take a walk on the peninsula St. Peter which has links to the philosopher Rousseau and above Biel in Magglingen/Macolin you can enjoy great views on a clear day.
But I think lake Neuchâtel has more to offer, Neuchâtel itself is great, the Latineum (history) museum, Creux du Van and Gorge de l'Areuse, Yverdon plus great beaches in Yvonand, the little town and castle in Grandson and Estavayer-le-lac might be the highlights on this lake. This region is called "land of three lakes", hence, lake Biel, lake Murten (with Murten and Avenches) and lake Neuchâtel are all connected with each other by boats. The region is also known for cycling.

Thankz for your input. I was thinking a nice relaxing week long+ stay in an apartment on one of the lakes in late Spring. We'll drive from the Oberpfalz and probably stay an overnight about halfway there and back. My French is very limited and my partners is rusty, but I think we'll get along. Looking forward to it. We're vaccinated and boosted. Any suggestions for a day trip into France? We've been to Switzerland several times and have been to most of the favorite tourist locations.