After our cruise ends, looking for a coastal area for 3 nights with nice biking!
It would be helpful to know where your cruise ends, and what time if year you will be there.
That said, if it were me, I would head up to Hoorn, which is a very picturesque village on the coast northeast of Amsterdam and bike from around there. One nice trip would be to bike from Hoorn to Enkhuizen, which passes through some very charming villages including Venhuizen, which has a tulip-picking garden (only if you're there during tulip season, of course).
Also, here is one website that might give you some guidance: https://www.komoot.com/guide/891826/cycling-around-hoorn
River cruise ends September 10 in Amsterdam!