Logic Masters Deutschland e.V.

This sudoku is a bit of an experimentation, but it does have a purely logical solution path.
This sudoku can be viewed as being a whispers sudoku, but where you need to draw in whispers.

We have the Anti-Knight constraint = No two cells a knight's move away can be equal.
Also the central 3x3 box is a magic square (the sums of each row, column and both diagonals are equal).

Moreover certain cells are coloured red. All red and white cells are given.
A cell is red if, and only if, at least one edge-adjacent cell is a divisor/factor or a multiple.
For example, if a cell containing 3 is red then at least one edge-adjacent cell contains a 1, 6, or 9.
Alternatively, if a cell containing 3 is white then no edge-adjacent cell contains a 1, 6, or 9.

The last condition can be interpreted in the terminology of whispers.
We say that two edge-adjacent cells are "whispering", if one of them divides the other one.
Then the red regions contain all cells that "whisper" with another edge-adjacent one.
However since no whispers are given, you will need to progressively draw in the whispers.

You can try this on Penpa-Edit. I hope you have fun discovering the whispers!
For some assistance, I have now added (below sudoku) a table of divisors and multiples (excluding itself). Table of Divisors and Multiples: