Hopefully it shouldn't be down for too long.
Its just a regular update to the engine room. For the geeks out there:
PHPBB Team wrote:The new version is a maintenance release of the 3.3.x branch which introduces a new helper function lang_js() for twig templates and resolves various issues reported in previous versions.
The fixes include, among others, further improvements on PHP 8 compatibility as well as some issues with migrations when upgrading or converting a board to the latest version of phpBB. In addition to that, some issues with the database handling for PostgreSQL, e.g. during backups, were also resolved.
We also introduced a bit of hardening in the form of disallowing specific UTF8 whitespace characters with zero or near zero width in usernames. These characters could cause some usernames to be confused with each other and hence we decided to specifically filter these.