Here's something I designed with red, white, and blue stars representing different multiples of five. A red star means the sum of the entries equals 10, white for 5, and blue for 15. Inside each cage, clues are placed between cells whenever possible so lack of a star gives important information as well. (No clues are placed on the major gridlines.)
Solution and a PDF can be found here: https://quadratablog.blogspot.com/2020/ ... uzzle.html