TYPO3 Core

From Slack:

can anyone help me to make the first step in using workspaces in 9.5.11?
It's a fresh composer based installation (including cms-workspaces ^9.5, cms-version ) with only a home page wich is visible in frontend.
After creating a simple workspace and switching to it before any editing, the preview only shows an Error-message:
Return value of TYPO3\CMS\Workspaces\Middleware\WorkspacePreview::renderPreviewInfo() must be of the type string, null returned
It would be very nice to get a little hint on it.
I've read this, yet: https://docs.typo3.org/c/typo3/cms-workspaces/master/en-us//Index.html

Dirk Steffens Sorry. I've found the mistake for myself. In typoscript there was set config.disablePreviewNotification = 1 - nobody knows why.
After setting in to 0 it runs like expected.