Unused elements detected on this page after TYPO3-Update
If you have not defined any backend layouts in TYPO3 so far, you will get the following error message after upgrading to version 9 when editing a page:
Unused elements detected on this page These elements don't belong to any of the available columns of this page. You should either delete them or move them to existing columns. We highlighted the problematic records for you.
To create a backend layout, follow these steps.
Go to the List module, select the entry path (globe) of your website, click on the "+" tick and then select Backend Layout:
Enter a title for the backend layout (optionally, an icon can also be uploaded, which can be a great help to the editor later in the case of several layouts). Now generate the number of columns required (arrows on the pen). In our example, there are two. In the old backend, four are displayed, but only "Left" and "Border" are required. Click the pencil (edit) for each column. Now give the two columns appropriate names ("Enter a name for the cell.") and IMPORTANT: the correct column ID ("The column position defines in which area the content is rendered in the frontend.").
In the old TYPO3 the default assignment of the four columns to the IDs was as follows:
far left ("Left") = 1
2. from the left ("Normal") = 0
3. from the left ("Right") = 2
4. from the left ("Border") = 3
You must therefore make an appropriate assignment (otherwise the content elements will later be displayed in the wrong place or not at all). In our example, these are "1" and "3", which we call "Left" and "Right" respectively (names do not matter). NOTE: In most cases you will need at least the "Normal" column. So the example here is a bit unusual.
The layout mask looks like this:
Now go to the page in question and select the page properties -> Appearance. Now select the layout you have just created under "Backend-Layout (this page only)".
Select "Backend-Layout (subpages of this page)" if the layout should also apply to all subpages.
The page is now displayed in 2 columns in the backend without an error message: