It is not possible to hide the standard attachment type within ticket's attachment facet, nor in other BOs such as Sales Orders, Quotes, etc..
SAP Cloud for Customer.
Reproducing the Issue
As example we are using the Ticket BO, the same is true for other business objects, such as Sales Orders, Sales Quotes, etc.
Go to the Service work center.
Go to the Tickets view .
Search for ticket XYZ1 (where XYZ1 is the ticket name) and open it.
Go to the Attachments facet .
Go to the Enter Adaptation.
Click on button Add ->Local file and select the drop-down option of Attachment Type field.
You can see, there is no option available to hide/delete the available attachment type from drop-down.
Currently it is not possible to hide the attachment type.
System will show all standard attachment types and it can not be hidden even via adaptation , this is current system behavior.
Attachment Type , Tickets , KBA , LOD-CRM-SRP , Service Request Processing , LOD-CRM-OPP , Opportunity Management , Problem