For Catalyst, how do we conditionally link with a Mac OS framework?

I wrote an iOS app that I've been able to run under Catalyst. It uses Bluetooth to communicate with devices (although this doesn't work in the Catalyst version for some reason; not what I'm asking about).

On the Mac, I want to use serial communications through a USB-to-serial interface. I have a framework for Mac OS that does this.

How would I link this framework into the Mac build created by Catalyst, but omit it from the iOS build?

Thanks for any insight.
For Catalyst, how do we conditionally link with a Mac OS framework?
 
 
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