TYPO3 Tipps:
Define layout in page content / content element
First of all, you should give the layout unique names that the editor can still recognise to some extent even after half a year of Typo3 abstinence.
To do this, we click on the root page and open the page properties. In the tabs there are the resources. There is a Page-TSconfig field. There, according to this pattern
entered. You can of course also outsource the TSConfig and provide it as .ts on the server. Then you have everything centralised. In the constants of the root template
<INCLUDE_TYPOSCRIPT: source="FILE:fileadmin/template/TypoScript/constants.ts">
defines the location of the file.
Now you can define the following or similar in the setup, which I also always outsource:
TYPO3 Extension: System / Typoscript
Version: <= 9.xx
Version: <= 9.xx