Timeout installing extensions
From Joomla! Documentation
Some websites updating to Joomla 3.9.23 installing or updating a extension could lead to a timeout.
This pertains only to Joomla! version(s): 3.9.23
What is the cause
The updated ZIP file decompression routine to support php 8 could lead to a much longer decompression time. Depending on the installed extension and webserver configuration this could result in an error because of a timeout.
How to fix
Update to Joomla 3.9.24. In the meantime replacing the content of libraries/vendor/joomla/archive/src/Zip.php with the updated version.