To determine the Salesforce Experience Cloud Guest User Cases created from the Contact Support Form, we can create a checkbox data type field and set the value to true from the Global Action used to create the Case records.

1. Create a checkbox field to differentiate Salesforce Experience Cloud Guest User Cases created from Contact Support Form.

2. Go to the Experience Cloud Site Builder.

3. Open the Contact Us Page.

4. Click the Contact Support Form. Find the Global Action used.

5. Go to Global Actions in the Salesforce Setup.

6. Open the Action used in the Contact Support Form.

7. Add new predefined value for the checkbox field in the Predefined Field Values Section.

Output: