An integrated mesh scene layer cannot be generated directly in ArcGIS Pro.
The source for an integrated mesh scene layer using the ArcGIS platform is through Drone2Map. For more information on Drone2Map, see Drone2Map.
Other vendors who publish integrated mesh scene layers (.slpk) to the I3S format include the following:
An integrated mesh scene layer package file can be displayed in ArcGIS Pro or ArcGIS Earth, and then uploaded to ArcGIS Enterprise or ArcGIS Online using the Share Package geoprocessing tool to publish it as a service layer. The input data type for integrated mesh scene layers is multipatch.