You can use Arcade to return a count of attachments. You can do this in ArcGIS Pro or ArcGIS Online. You could also choose to apply this to symbology to see which features have attachments, or you could use this in a field calculation to write the total number of attachments to a given field. If you don't want to modify your schema by adding a field for this, in ArcGIS Pro you could create a selection of features with attachments and then export a csv file from that. Hope that helps.
// Returns the number of attachments associated with the feature
Count(Attachments($feature))
Here is a link to the Arcade documentation for Attachments.
