JSON Form formatting: Unable to use the calculated column value in header/footer layout customization

Target SharePoint environment

SharePoint Online

What SharePoint development model, framework, SDK or API is this about?

Declarative list formatting

Developer environment

None

What browser(s) / client(s) have you tested

• 💥 Internet Explorer
• 💥 Microsoft Edge
• 💥 Google Chrome
• 💥 FireFox
• 💥 Safari
• mobile (iOS/iPadOS)
• mobile (Android)
• not applicable
• other (enter in the "Additional environment details" area below)

Additional environment details

No response

Describe the bug / error

Unable to use the calculated column value in header/footer layout customization using JSON list formatting. Calculated column value can be used in column/view formatting.

The calculated column value is available in the page context but it is not shown in form header:

Steps to reproduce

1. Create a simple calculated column in SharePoint list. For example using formula: =[Title]
2. Open list form > Edit form > Configure layout > Header
3. Add JSON in below format and Save

{
    "elmType": "div",
    "txtContent": "='Value: ' + [$CalcPH]"
}

Expected behavior

Customized list form header/footer should show the calculated column value without any problem.