Unable to create multiple actions with Make Read only for different fields based on user group

May consider below workarounds:

1. Go to Project Settings > Work Item Types.
2. Select the work item type (e.g., User Story, Bug).
3. Click Rules.
4. Create your rule with the condition:
   Current user is not a member of [Your Group].
5. Add one “Make read-only” action for a field.
6. Save the rule.
7. Now click Export Process (if using Inherited Process) or use Azure DevOps REST API to retrieve the rule definition.
8. Edit the JSON to include multiple fields under the actions array:

"actions": [
  {
    "actionType": "MakeReadOnly",
    "targetField": "Field1"
  },
  {
    "actionType": "MakeReadOnly",
    "targetField": "Field2"
  }
]

9. Re-import or update the process using the API or admin portal.