Logic Masters Deutschland e.V.

This is one large puzzle, consisting of four different variants of 6x6 sudokus, which are all linked together by numbers in grey circles.
A number in a grey cell is the sum of the outside clues for the adjacent puzzles. Digits used for this sum may not repeat.

Normal 6x6 sudoku rules apply to all sudokus, so every row column and region must contain the digits 1 to 6.

Additional rules per variant:
Edge sum: Clues outside the grid indicate the sum of the first two digits in the corresponding direction.
Sandwich sum: Clues outside the grid indicate the sum of the digit(s) placed between 1 and 6 in the corresponding row or column.
Grey cells sum: Clues outside the grid indicate the sum of the digit(s) in the grey cell(s) in the corresponding row or column.
Next-to-6 sum Sudoku: Clues outside the grid indicate the sum of all direct neighbours of the digit 6 in the respective row or column.

A number in a grey cell is the sum of the outside clues for the adjacent puzzles and digits used for this sum may not repeat.
For example: When 10 is in the grey circle between the Edge sum and Sandwich sum sudokus and the digits 2 and 3 are between the 1 and 6 in the Sandwich sudoku, then 2 and 3 may not occur in the first two cells in the corresponding direction of the Edge sum sudoku and therefor those cells must contain 1 and 4.

The puzzle is also available on Penpa.

I think the logic and the interaction between the puzzles are really nice. I hope you like it as well. If you struggle finding the logic of this puzzle, find some hints here. But try it yourself first of course ;) Enjoy solving! :)