US international keyboard layout with german umlauts for Windows.
Clone the repo and use setup.exe or use the .klc file with Microsoft Keyboard Layout Creator.
AltGR + A for Ä
AltGR + O for Ö
AltGR + U for Ü
AltGR + s for ẞ
and
AltGR + 2 for €
Use Shift + AltGR for respective upper case.