Go to Flow Designer
Select application other than global
Create a new Action.
Add an input parameter called Document, select Reference.sys_attachment
None is found.
On all versions that has flow designer plugin installed
due to the system property - sn_flow_designer.allowed_system_tables
This was done on purpose by internal team so that users will be very careful when updating the action.
Please be very careful when using sys_attachments in action and flow.
So, its needs to be connected with sys_attachment_doc to work.
Open the below property and remove sys_attachment from the property sn_flow_designer.allowed_system_tables.
As such there property which has a very confusing name sn_flow_designer.allowed_system_tables which in reality is the opposite of its name. (Something we need to change).