Logic Masters Deutschland e.V.

Previous Dutch Flat Mate Puzzles
This has been a weekly series since '18 Oct 23'. Here is a spreadsheet link for all the previous puzzles in the series, which also has a few teasers for upcoming constraints/guest setters in the series (subject to change).
This alternative link offers a limited LMD search for Dutch Flat Mates.

Special Thanks
The inspiration for this puzzle is Quadsumes by SennyK.
Whilst setting this puzzle, I somehow didn't even realise that it was two constraints combined until after I had a draft I was happy with. I briefly tried to set a Dutch Flat Mates puzzle with just 'Sum Dots', but failed to find any logic I liked.

To play the puzzle, please click the image:

Initial Setter Difficulty: 2.5 / 5

Normal Sudoku rules apply
Place the digits 1-9 so that they do not repeat in any row, column, or 3x3 box.

Dutch Flats
Every 5 in the grid must have a '1' directly above it or a '9' directly below it. It may have both, but it doesn't need both.

Quadsumes
Digits in cells touching a gold sum dot must sum to the indicated total. Digits may repeat if allowed by other rules. Additionally, both digits in a sum dot must appear separately within the four surrounding cells.

Hint to start

The clues in the 10s and 20s have different universal properties. Sudoku (and basic math) is your friend to help fully resolve the 22 and 23 clues, as well as some easy onwards progress. You soon find happy 5 spots are quite limited.