How to enter @ and € on a German MacOS installation?
If on the Mac you set the Input Source to &quot;German Standard&quot; (and not &quot;German&quot;), then you will have @ produced by Option/alt Q and € by Option/alt E.  That may be how your 3rd party keyboard is printed.
The layout shown in HT201794 reflects an Apple keyboard which corresponds to the &quot;German&quot; input source.  The newest Apple keyboards correspond to German Standard.