Unable to use inactive picklist values in Report or List View filters

Create a Formula Field

Add a custom formula field to the target object that retrieves the text value of the picklist.

Replace 'Picklist_API_Name' with the API name of the picklist field on your object (for example, 'Stage' for the Opportunity Stage field would be written as TEXT(StageName)).

How to filter: Use this new formula field in your report or list view filters. Since it is a text field, you can manually type in the inactive value to filter by it.

Filter to retrieve only inactive values

To retrieve records with inactive picklist values, add the picklist field as a filter, set the operator to 'not equal to,' and select all currently active values. Any records not matching the active values — including those with inactive values — will be returned.