Hello there,
I am aware that you can select a (as in singular) key that is not on the keyboard from the dropdown, but I need a way to set it to "⌘=". I don't have an equal sign key on any of my keyboards (different language) is there a way to do that? Maybe use a variable or something?
Thanks for the help in advance 
I think so. There's a feature in macOS called "Keyboard Viewer" which displays an image of a keyboard on your screen and you can press keys that you don't have using your mouse.
Open System Settings. Type "Viewer" in the search box. Click the button at the top called "Show Input Menu in Menu Bar". Then in the menu bar you will have a new icon that will let you click on "Show Keyboard Viewer." Then you will see a keyboard on your screen where you can press the equal key with your mouse.
I suspect this will work for you, but I'm only 90% sure. I can't test it because I don't have your keyboard type.
What language? Which keyboard layout for that language? Is = not lurking behind an Option key combo somewhere?
You could use something like Karabiner to re-map any key to '=' temporarily.
Total guess, but the name Karl Dietrich leads me guess that you have a German keyboard.
According to this:
https://community.wolfram.com/groups/-/m/t/1558441
Shift+0 should work to get '='
You are right but unfortunately that does not work. I tried to remap a key but it turns out Keyboardmaestro does save the key and not the symbol so If i map the +-Char to =-Char then in the background it will save something like key "30" and not the char. So after I turn it back to "normal" it also reverts to +-char.
So, asking again...
What language? What keyboard layout for that language?
It's quite unusual for a "western" language to not have an = typeable by some key combo -- we just have to work out which.
If it really doesn't exist -- why do you need to "Type Keystroke" it? Perhaps there's some other way to do what you want?