Hey,
I'm trying to remap some of my numbed keys in AutoCAD to do some other things for me.
I'd like to use the "," key to type "." and the "Return" key to type ",".
That's what I tried, sending a "Delete" before the "." would work but is there a way to just block the keyboard sending the "," to AutoCAD?
When trying to rebind "Return" in the numbed the same way the "Delete" way doesn't work anyways.
Thanks for your help! 
Try creating a Macro Group for macros that are only active in AutoCad using File > New Macro Group. Set the new Macro Group to Available In These Applications: AutoCAD 2021.
Once the AutoCad Macro Group is created, move the macros to that group or re-create them there. They should work without needing to add the Delete step you described. Like so:
**Note just for future reference: Return and Enter keys are not the same even if sometimes they behave the same. You specified Return in your description but showed Enter in your image, so create macros matching what you need used or simulated.
My bad for confusing Return and Enter.
The solution you show would work for every , / Enter on all Keyboards.
I just want it to work if I use the numbed keys on my external keyboard. Thats why I used the device key trigger. But that way the original function does not get blocked. Any idea how to solve this?
as @NaOH mentioned, if you create a Macro Group, and set it to only be active for AutoCAD, it should change the behavior of the NumPad when you have AutoCAD at the front.
It will only change the behavior of the numpad, or any external keyboard that uses exactly the same configuration in the USB Device, in your case, the "MX Keys Mac" keyboard.
sometimes, an app doesn't "swallow" the key
Look closely - @Marvinha's macros are already in an AutoCAD group.
@Marvinha, here is one of my macros that remaps a keypad key:
Ignoring the Semaphore action, the only real difference is I'm using an Apple Keyboard with Numeric Keypad. Maybe the issue is to do with your use of a non-Apple keyboard?