In the past, you could add new tabs to records by creating a new field in Database → Fields (legacy tool), which is distinct from the present day Database → Fields.
If your database uses fields with Tab values to create tabs on records, you can migrate to the current best practice, which uses forms. When you migrate, you must ensure that the source key of exports and filters in existing queries continues to function as intended.
To migrate to form-based custom tabs:
Go to Database → Fields (legacy tool).
Select a field that represents a custom tab.
From the Category list:
If the value for Category is the same as the value for Tab, you don’t need to do anything.
If the value for Tab is in the list, select it.
If the value for Tab is not in the list, select Other and enter the Tab value in the text field.
From the Tab list, select the blank value.
Select Save.