I just released two new versions that contain bugfixes: 3.0.1 (for TYPO3 v11/v12) and 2.1.1 (for TYPO3 v10/v11).
Both patches are related to the hook typolinkModifyParameterForPageLinks as well as the PSR-14 event ModifyPageLinkConfigurationEvent (from TYPO3 v12), which are used to set the human-readable fragments for links in the RTE and in backend fields of type inputLink (e.g. the header link).
Check for configuration in multi-domain setup
In TYPO3 installations with multiple page trees, the extension may be not actively used on every website.
However, both the above-mentioned hook and the PSR-14 event are registered globally and therefore are always processed. If the TypoScript of this extension is missing in the page tree and a content element is linked in the RTE or inputLink field, this caused PHP Warning: Undefined array key "tx_contentslug. in ... with PHP 8.
A null coalescing operator (??) in this line prevents this problem from now on.
Since the older version branch 2.x supports TYPO3 v11 and is therefore also affected (TYPO3 v10 generally has no PHP 8 support), I have also released version 2.1.1.
Check for existence of linked content element
If the content element linked (in the RTE or inputLink field) does not (or no longer) exist, PHP 8 used to throw an exception. The issue is limited to extension version 3.0.0.
In version 2.x, a query still exists whether a value is set in the fragment field. This was removed in version 3.0.0 to make the usage more flexible.
Many thanks to David, who reported this problem and also supplied a pull request!