A few more items from running 8.0.1 on PHP 8.4, in case they help 8.1.0:
1. libs/ubbthreads.inc.php line 917 passes E_STRICT to error_reporting(). E_STRICT is deprecated in PHP 8.4, so it logs a deprecation on every request — about 99.7% of our forum's log lines. Removing E_STRICT from that line fixes it. That runtime error_reporting() call also overrides php.ini/.user.ini, so we can't quiet it from config.
2. The bundled Smarty predates PHP 8.1's nullable-parameter rule (deprecations in smarty_resource.php, smarty_internal_data.php, Smarty.class.php). A Smarty refresh would clear them.
3. iOS Safari: the head emits a viewport without shrink-to-fit=no, and a second viewport from a theme competes with it, so tables shrink after rotating. One viewport tag with shrink-to-fit=no fixes it.
4. ultimatebb.cgi (legacy stub) prints "HTTP/1.1 301" — under CGI it needs "Status: 301", so old links get a 500.
5. credits.md still says 8.0.0 after the 8.0.1 patch.
6. Control Panel > Paths & Database can't save new DB credentials once the old ones stop working (the save needs a live connection), and fails silently.
7. ubbthreads.php?ubb=grabnext returns 200 even with junk parameters, giving search engines one extra URL per post.
Thanks!