When sharing feature layers as copies in a distributed collaboration there is currently a size limitation of 1 GB; if the feature layer is over 1 GB the layer is shared as a reference rather than as a copy (FAQ Link). I currently have layers in my geodatabase that I would like to share as copies to ArcGIS Online but cannot because of the number of feature attachments in the layer. As a possible solution to this problem, I would like to propose that the distributed collaboration settings be enhanced to include attachment controls similar to those that are found in the Field Maps interface in ArcGIS Enterprise:
With these controls provided at the collaboration, group, or service level users could decide how features and attachments are synchronized with the parent organization.