There are two ways a new, non-MARC Instance record can be created in Inventory, "New" and "Duplicate"
Only non-MARC Instance records can be edited directly within Inventory
Steps
Open the Inventory App
Select the "Actions" menu in the upper right pane
Select "+ New"
Fill in the required fields and other fields needed for identification/batch match
Select "Save and close" in the lower right
Expected Result
New instance record displays in the right pane
Preconditions
An instance record similar to the one desired already exists in Inventory. It may have source MARC or FOLIO.
Steps
Expected Result
New instance record displays in the right pane. Note that even if the record you duplicated had source MARC, the new Instance has source FOLIO.
Preconditions
An instance record exists with no underlying MARC data.
Steps
Expected Result
The instance record displays in the right pane with edits as made