I’d like to go on a bike day trip from a city to surrounding small towns, not a multi day trek just one or two day trips of cute towns and nice views. Are there any that come to mind?
You would have to drill down on bike rental availability, routes, etc., but I would suggest looking into the Alsace region of France. There are many small villages close together that are extremely different and interesting to see along with some wineries.
Amsterdam would be my suggestion. It has long-standing bicycle-friendly culture and hundreds of beautiful, level, and dedicated bike paths that radiate out from the city. There are bike shops at the central train station from where you can peddle down to a nearby pedestrian/bike ferry. Once across the river you'll be in the countryside and can literally spend days exploring the little towns to the north.
The bike shops all sell an excellent map of the local bike paths - costs a couple of Euros and is well worth the investment.
You can bike in and around Bruges. We have done 2 multi day bike trips. One around Lake Constance. You could easily rent in Constance and bike in a few directions from there. The 2nd was From Metz France to Cochem Germany along the Mosel mostly along a wonderful dedicated by path. There is also great biking along the Rhine.
I took my Grandson on a bike trip when he was 15. We rented bikes in Amboise. Got a bike trail map from the IT office. The trails are wonderful, along the river, thru sunflower fields, forests and gardens to Chateaus for a tour and great lunches. Ride back or take the train. Just wonderful. I also did a bike riding trip along the Rhine and Mosel, ride down the river, see a castle and ride the bike back or take a ferry. J