I have similar problem with Ja Stark on joomla 4.2.8 - php 8.1 - t4-system-plugin_2.2.6
There errors:
Deprecated: preg_match(): Passing null to parameter #2 ($subject) of type string is deprecated in /home/paolofio/public_html/ilbardelcastagno.it/templates/ja_stark/html/layouts/chromes/T4Section.php on line 18
Deprecated: htmlspecialchars(): Passing null to parameter #1 ($string) of type string is deprecated in /home/paolofio/public_html/ilbardelcastagno.it/templates/ja_stark/html/layouts/chromes/T4Section.php on line 24