TYPO3 Core

Addendum: my suggestion would be to set up a checkbox "exclude from hreflang" in the site management for the languages. That way you could control this specifically for individual languages and you don't have to deactivate a language completely if it is still under construction on the one hand, but on the other hand should be made available to decision makers without BE access. The global unset for hreflang would then also no longer be absolutely necessary.

What I also don't like about a complete deactivation of a language: if for each language a separate domain is used and a language is hidden for the time being, then you only have a preview if you are logged in at the same time under the same domain in the BE. If you call the domain by mistake without being logged into the BE, a 404 is created. If the error handling is set to "show content from page", then the 404 content is also not accessible and an error entry is created in the log.

The Hook was replaced by an PSR-14 Event. See: #86614

So there is no possibility to generally unset the generation. What you could do now is register an own listener which is executed after and unset the HrefLang tags.

However the documentation should be updated for this case.

I think that, apart from the above example, there may still be other cases where it is necessary to deactivate the hreflang. For example, if you have a news module with a page browser that goes over 10 pages in one language but only 5 in another. So far the hreflang of page 10 would lead to a non-existent page 10 of the other language. So it would be better to deactivate it and it would be nice if this could even be done via TypoScript:

[request.getQueryParams()['tx_news_pi1']['widget_0']['currentPage'] && request.getQueryParams()['tx_news_pi1']['widget_0']['currentPage'] > 0]
    page.config.hreflang = 0
[global]

So even an integrator could deactivate it, because the hook is rather something for developers.

For now I updated the docs (see review), but I also created https://forge.typo3.org/issues/93188 to work on a more easy way to disable the rendering of those tags.

Patch set 2 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/c/Packages/TYPO3.CMS/+/67315

Patch set 3 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/c/Packages/TYPO3.CMS/+/67315

Patch set 1 for branch 10.4 of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/c/Packages/TYPO3.CMS/+/67294