SPFx 1.21 RC `flexibleLayoutSizing` value of `supportsDynamicResizing` in web part's manifest

What type of issue is this?

Question

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

💥 SharePoint Framework

Target SharePoint environment

SharePoint Online

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

• browser version: 135.0.7049.85
• SPFx version: 1.21.0-rc.0
• Node.js version: v22.14.0

Issue description

In the latest SPFx version 1.21 RC the support to flexible layout was introduced.
I've checked the release notes where the following code sample is shown:

"flexibleLayoutSizing": {
    "supportsDynamicResizing": true,
    "defaultRowHeight": 10,
    "defaultColumnWidth": 10
  }

However I don't understand how the supportsDynamicResizing should work.
I've tried changing it, repackaging the solution and redeploy it but it doesn't seem to have any effect.
Can someone help me understand how this should work? Is the support to this configuration still in the rolling out phase?

Thanks in advance!