See :issue:`84324`
All methods not used as entry points by :php:`TYPO3\CMS\Backend\Http\RouteDispatcher` will be removed or set to protected in v10 and throw deprecation warnings if used from a third party:
- [not scanned] :php:`main()`
php: initClipboard() php: finish()
Calling one of the above methods on an instance of :php:`FileController` will throw a deprecation warning in v9 and a PHP fatal in v10.
The extension scanner will find most usages, but may also find some false positives. In general all extensions that call methods except :php:`mainAction()` are affected.
In general, extensions should not instantiate and re-use controllers of the core. Existing usages should be rewritten to be free of calls like these.
.. index:: Backend, PHP-API, PartiallyScanned