Breaking: #97451 - Removed BackendController page hooks¶
been removed in favor of a new PSR-14 event
BackendController->addCss() method has been removed without replacement,
as it is no longer used.
Any hook implementation registered is not executed anymore in TYPO3 v12.0+. The extension scanner will report possible usages.
All TYPO3 installations using this hook in custom extension code.
The hooks are removed without deprecation in order to allow extensions to work with TYPO3 v11 (using the hook) and v12+ (using the new event).
Use the PSR-14 event as an improved replacement.