as stated in the other bugticket https://forge.typo3.org/issues/87260:

Situation: Language EN-US falls back to EN-GB, Default Language 0 is DE-DE.
Page exists in DE-DE and EN-GB (free mode), but not in EN-US:

Now you call the page in EN-US, which completely falls back to EN-GB:

If you have "Jump" Contentelements, which link to other content-elements (not page links, which work fine) on the same or other pages, then NO links (as $record = 0 is returned) will be created. This breaks the fallback chain and language handling of bigger sites totally. No content fallback to languages other than default can be done.

Your fix doesnt solve the problem. I am talking about a frontend request to a site language, which has a fallback language OTHER than language 0 (default). In this situation, the LinkHandler returns $row = 0.

The tt_content record which is running through the handler is the one of the fallback language (!), which ofc has no l10n_parent and no _LOCALIZED_UID as it is the fallback record. This mis-understanding of language fallback kicked in with the introduction of the Site module and its placemnet in the core-logic. In former TYPO3 versions, multi-stage language fallbacks could be done with the CORE or additionally with TemplaVoila and with a slight patch even in extbase.

The site module and new routing is pretty broken, if you move out of basic language handling. It also can't handle mixed mode of page translations for extbase plugins accordingly.

I would suggest to abandon the "fix" in https://forge.typo3.org/issues/87260 completely.

My proposal für a fix would be:

    if (
        empty($overlay['_LOCALIZED_UID'])
        && empty($overlay['l10n_parent'])
        && !in_array($record['sys_language_uid'],$languageAspect->getFallbackChain())
       ) {
            $record = 0;
      }

So if it is NOT a record of a fallback-chain language, then abandon the link. Otherwise, its correct to link to the element.

The current behaviour is also broken in case you don't have a default language version of a certain record which you'll link.

1. Create two languages
2. Create a record in 2nd language (not default)
3. Link to that record from within 2nd language

The link will not exist as there is no default record and no localized uid.

@Frank Gerards can you check whether https://review.typo3.org/c/Packages/TYPO3.CMS/+/82775 solved the issue?