MY OWN SOLUTION:
The problem I had was, that I added the extension editorconfig to my vscode, but didn’t install the npm package for it. So it’s not enough, to add the extension only to your vscode, you have also to install the package, so it could run.
I installed the npm package global like this: npm install -g editorconfig
After that I added the extension and enabled it. Now it works perfectly.
Required npm package: https://www.npmjs.com/package/editorconfig
Required vscode extension: https://marketplace.visualstudio.com/items?itemName=EditorConfig.EditorConfig