It is not possible to add an attachment while creating a new instance of an object in the Modern UX grid view. It is possible to add it once the instance is created, but if the attachment attribute is required, it will not be possible to create new instances from the grid (i.e.: using the '+' button)
Steps to Reproduce:
Expected Results: After adding all required attributes, including the attachment, the new project is created.
Actual Results: It is not possible to attach a file unless the project already exists. As the attribute is required, the project is not created.
Release : 16.1.0
This is working as designed. We cannot add an attachment attribute without creating the instance first. To avoid this, the attachment attribute during creation is disabled.
Grant the 'Create from Template' access right instead of the 'Create' right so that the user is forced to create the project from a template. Remove the 'Create' access right. In this usage, the 'Create Modal' will appear and any Studio-Required fields will show up automatically for the user to fill in at the time of creating the project.