I don't think you can sort the tours by activity level, but I think most of the tours are listed as moderately to very active. On any tour you can usually adjust the physical challenge level to some degree - e.g., don't go on a long hike in your free time (or do).
I'd second CWSocial's suggestion about the Turkey tour. Not only is it physically active with walking/stairs/etc. but you also need stamina for the long bus days as well as the culture shock aspect (in a good way). In that regard, you might want to go on some of the longer duration tours if you have the time. You can filter tours by length (on the tour page in the find a tour box, there is a tab for sorting tours by duration https://www.ricksteves.com/tours)