The reason it’s asking you for more, is because the expression you’ve entered doesn’t evaluate to the correct ‘type’ for the field.
So it’s waiting for you to continue the expression until the expression’s value matches the expected type.
For example, if you have a field that has the type ‘Text’ and you enter the expression Current User it will ask you for more because the expression does not yet evaluate to a text. Once you continue the expression to output a text value it will be accepted.
In your first example, you’ve set the Type of things for the workflow to run on to be ‘Inventory’.
Therefore, the list to run on MUST be a list of Inventories…
but your expression is NOT a list of Inventories, but rather a single Inventory File (which is neither the correct type, nor a list) - hence why it’s red, and is expecting you to continue the expression until it evaluates to a list of Inventories.
Then, you’ve entered an expression of This Inventory in the upload file field. The value of the expression is an Inventory.
I’ve got no idea what the expected value of your ‘Upload file’ workflow parameter is (perhaps it’s ‘file’?), but it’s obviously not Inventory, hence the error again, as the expression is not complete.