You can create read-only fields set by External Data for Jira Fields that users or agents cannot edit in the work item. With this guide it’s possible to for example lock a Search Field after the initial creation or create read only text fields, read only user fields, or read only date fields with Dependant Fields.
The setup varies by Field Type, but the basic process is the same: remove the field you want read-only from the Edit and/or Create Work Item Screen of the relevant spaces and work item types.
First, create a new screen by going to Settings (⚙️) > Work items > Screens. You can create a screen from scratch using the Add screen button or copy an existing screen via the Actions (···) button. Remove the External Data field(s) to be read-only from all tabs on this screen.
Next, assign the new screen to the relevant space screen scheme(s). The easiest way is via Space settings > Work items > Screens. Click the Edit (✏️) button on the relevant screen scheme.
If you have not associated different screens with the Work item operations, click the Associate a work item operation with a screen button. Add the new ‘read only’ screen to the Create work item or Edit work item operations, or both. Choose based on whether you want the field uneditable always or only after creation.
If you already have different screens for specific Work item operations, click Edit and assign your 'read only' screen.