on a monolingual site with php 8.0.10 I could not replicate this

Was the number of folder > 0?

Mine is a multilingual site too and it happens also when I choose English as language.
I found this in the ajax request answer, seems to be the plural language string.

-- libraries\src\Language\Text.php(251): sprintf('Globales Freige...', 2)
-- administrator\components\com_checkin\src\Controller\DisplayController.php(120): Joomla\CMS\Language\Text::plural('COM_CHECKIN_N_Q...', 2)\n
-- \libraries\src\MVC\Controller\BaseController.php(730): Joomla\Component\Checkin\Administrator\Controller\DisplayController->getQuickiconContent()

it was 1

Then it is another language key which does not replace the %D

COM_CHECKIN_N_QUICKICON_SRONLY="Globales Freigeben: %D Tabellen haben gesperrte Einträge."

I did locate another problem though - note the count. only the first image has the correct count

The first one counts the number of records, the quickicon counts the number of folders. I agree that this is not self explaining.

folders is wrong. you are checking in items

Can you open another issue then? Then it will not be forgotten if this one will be closed.

will do

The german language strings use %D instead of %d as placeholder for variables in this language file (com_checkin.ini). With php 7 this does not matter but in php 8
@tecpromotion @zero-24.

Solution in the german language file or in the sprintf function of text.php (in case of other languages who also use %D)?
Regex is not what I want to touch ...

fixed in joomlagerman/joomla#2253
thanks @chmst

So I close this for now as the bug is fixed in the german language file. Thanks @tecpromotion