Instead of info.magnolia.ui.framework.layout.TabbedLayoutDefinition, you can now use Magnolia 5 UI form tabs in Magnolia 6 UI. To do so, add $type: tabbedForm to your form definition:

$type: tabbedForm
tabs:
  general:
    fields:
      foo:
        label: foo
        $type: textField
  otherTab:
    fields:
      bar:
        label: bar
        $type: textField
        required: true

The above tabs should be defined under the form node. The i18n keys from Magnolia 5 UI are not supported in this form.

Roman: "It's a form type forcing a specific layout type". Page to update: https://docs.magnolia-cms.com/product-docs/6.2/Templating/Dialog-definition/Form-definition.html

Include notes on what the i18n keys are.

(Some information here: https://jira.magnolia-cms.com/browse/MGNLUI-6771?focusedCommentId=271224&page=com.atlassian.jira.plugin.system.issuetabpanels%3Acomment-tabpanel#comment-271224)