Hi, I use/sacrifice Mixer 3 (and in Cubase 12 Mixer 4) for my macros.
That way I do not have to worry about the Main Mixer Window being open or not when I trigger macros.
The Mixer you choose to use for the macro should not be used for any thing else other then the macro in your normal workflow.
Example of how I program a macro when I need the mixer to be focused for it to work.
I used this a while back to solve an issue I had with bypassing Inserts on selected channels.
If you are interested, you can read more about it here.
Workaround to Bypass Inserts, Sends, Channel Strip, EQ and Cue Sends with short key
Maybe this is of use to you.