Logic Pro - how to set different inputs for Mic and Guitar

Hello! I have a question - and none of the million YouTube videos nor chat gpt can help - so I don't know what I am doing wrong:

I have my e-guitar plugged into the Mustang LT40S Amp, which is connected to my Mac vía USB. My mic is plugged via XLR into my Steinberg UR12, which is also connected to Mac via USB. I also use headphones plugged into the Steinberg. Using Logic Pro trial - when I create my Audio Track, I chose "Input 1" which is the input 1 on Steinberg for Mic, chose the device "Steinberg 12" and also chose "Steinberg 12 " for Output - everything works.

Then I create the second track for my guitar - here I am not sure which Input to take, Input 2? or None? and then I chose my device: mustang as input - and output Steinberg 12. AS soon as I create the second track (in this case guitar) - the mic track also jumps to the same setting, meaning it also uses the mustang as Input - tried it the other way around - same result. I tried to lock the first track and then create the second one - same s**t. I created an aggravate device in Audio midi - but then nothing works...

What am I doing wrong!!! Sitting since hours but I can hear either my mic or my guitar - not both ....anyone knows what could be the problem here?

thanks so much in advance