TYPO3 Core

As i understand it, the issue could be solved by backporting this feature:
https://docs.typo3.org/c/typo3/cms-core/main/en-us/Changelog/12.0/Feature-97737-PSR-14EventsWhenPageRootlineInFrontendIsResolved.html

Sadly i can not upgrade to V12 in the short-term, too many of our packages do not have support for V12 yet and the project was just upgraded to V11.

Did you recently upgrade from TYPO3 v8 (or earlier) to TYPO3 v11?

The mentioned behavior (sending 403 for unauthorized access) is the default behavior since at least TYPO3 v9, there are tests for that, documenting this behavior, see https://github.com/TYPO3/typo3/blob/9.5/typo3/sysext/frontend/Tests/Functional/SiteHandling/SiteRequestTest.php#L447-L471

In order to handle this individually, one can use the corresponding settings in the site configuration, e.g. statically or using an individual PHP class implementing PageErrorHandlerInterface, see https://docs.typo3.org/m/typo3/reference-coreapi/10.4/en-us/ApiOverview/SiteHandling/ErrorHandling.html

In case this ticket is about proper linking, you might consider using TypoScript property config.typolinkLinkAccessRestrictedPages, which references to the login page in case an access protected page is linked and the current visitor does not have permissions, see https://docs.typo3.org/m/typo3/reference-typoscript/main/en-us/Setup/Config/Index.html#typolinklinkaccessrestrictedpages

Philipp Wrann wrote in #note-1:

As i understand it, the issue could be solved by backporting this feature:
https://docs.typo3.org/c/typo3/cms-core/main/en-us/Changelog/12.0/Feature-97737-PSR-14EventsWhenPageRootlineInFrontendIsResolved.html

Sadly i can not upgrade to V12 in the short-term, too many of our packages do not have support for V12 yet and the project was just upgraded to V11.

I don't think this is required, since the new PSR-14 events are basically replacing the hooks that existed already before. Thus, it's possible to use those hooks prior to TYPO3 v12.