Fill the empty cells with numbers from 1 to 9, ensuring that each row, column, and 3x3 square does not have repeated numbers. In groups marked with dashed lines, the sum of the numbers should equal the specified number. Knowing these rules, you can easily find missing numbers step by step if most cells in a group are filled.
At the start of the game, you can use the fact that the sum of all numbers is 45. For example, if several shaded areas fit entirely in one group or in several adjacent groups, except for one cell, you can determine the number in that cell by subtracting the sum of these areas from 45 (or from 90, 135, etc. if checking multiple adjacent groups).
As in regular Sudoku, placing candidates in cells and gradually eliminating them helps find missing numbers. The set of possible candidate numbers for dashed groups with small or, conversely, large sums is very limited, for example, 16 is only 7 and 9, and 4 is only 1 and 3. Having the same pair of candidates in two cells belonging to the same line, column, or square allows you to exclude these candidates from other cells in the same area. Set possible candidates and gradually eliminate impossible ones, step by step, to solve the entire puzzle.