Create excel from local data

You can do this by converting a datasubset to base64 and then converting base64 to an Appian document. You need to be careful doing this as these plugins can really harm your environment because of how much text they generate. Look at the Excel Tools plugin to find the function 'exportdatasubsettobase64' and then look at the plugin 'Base64 document conversion' to use the smart service. I recommend not saving base64 in a process variable and instead calling the function to exportdatasubsettobase64 within the other smart service. You should also set the process to terminate upon completion and to delete after 1 day

Does this need to happen in process or does the list appear on screen and the user clicks a button to export?

To add, many of us are still relying on the deprecated Export CDT to Excel service within the Excel Tools plugin for this functionality.  Would be very nice to see this OOTB one day! :)