I'm trying to set up a secondary keyboard to use for macros and I'm running into the issue that when using "Triggered by(...) This device key" so when I press a key on only the secondary keyboard it runs the macro, the key that I press still goes through. I want it to not go through to any app, only to KM so I can run the macro.
Karabiner doesn't have all the features I want. I can't make a key do cmd + s or make it type something.
Yes you can but you shouldn't.
Let KE manage KeyBinding and KM do the Keyboard-Shortcut thing.
If you want do all the thing in one software, you should try Hammerspoon. I was using Hammerspoon years ago trying to replace Alfred + KM + some other softwares and it was buggy then I gave up.
Do one thing and do it well.
-- Unix Philosophy.