After you have saved a layout, you can make edits to it by selecting the Layout tab. Make sure to click the "Save layout" button to complete your edits.
Layout Builder
If content allows overriding the default layout, a Layout tab will be available near the Edit tab.
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Drupal's Layout Builder allows content editors and site builders to create grid layouts for displaying content. Users can customize how content is arranged on a single page, across types of content, or even create custom landing pages with a drag-and-drop interface. Layout Builder is turned on by default for Basic pages on SCLS-supported library websites.