This type of read-only custom field has a value which is dynamically calculated from a custom text expression. It can be used to show a text composed from one or more field values returned by field codes.
You can also create any custom text value depending on the values of other fields in the current issue or in any other issues (linked issues, sub-tasks, epics, stories, JQL selected issues, etc).
Learn more about working with Texts.
Configuring a calculated text field is straightforward. You just have to configure a valid parsing mode and add a parser expression, which will "calculate" the output.
Create a new Calculated Text Field (by JWT) custom field and name it properly
Providing a description will help you to identify what the custom field does but this step is optional
Add a valid parser expression which will "calculate" the output.
Usually field codes will be used for this purpose.