You can see combined desktop and mobile performance data for your Messages (excluding Full Screen, Undercut and Notifications) In that case, you can simply set up one message without applying 'Device type' audience targeting. This allows you to monitor the performance of that single message.
Alternatively, if you would like to monitor the desktop and mobile performance separately, you’ll need to duplicate your message and apply different 'Device type' targeting to each version. This method provides a clearer picture of how many visitors are seeing and interacting with your message on both channels.
You might discover that one channel performs better than the other, which can inform further optimizations to enhance the website experience for both types of guests.
Here's how to set up a mobile and desktop version of the same message
In the Message Builder, set up your message as usual. Navigate to the Audience tab, select Device targeting, and choose Mobile device only.
Once you’re satisfied with the content and design of your message, save it as a draft. Then, return to the Message Manager and click the plus sign on the right-hand side of your message to duplicate it.
Duplicating the message will instantly create a new version with the original name followed by 'copy'. It's advisable to rename the duplicate to include 'Desktop' and the original to include 'desktop' for easier differentiation.
For the duplicated message, go to the Audience tab and switch the Device type targeting to Desktop traffic only. Check the Design tab to see how your message appears on mobile and make any necessary tweaks to ensure it looks as appealing on mobile as it does on desktop.
Once you are satisfied with both versions of the message, publish them. You will then be able to compare the performance of your mobile and desktop messages in the Message Manager.