After clean install both set:
Joomla 3.10.2 + T4 plugin 2.0.7 + t4_blank_tpl_1.1.3
Joomla 4.0.3 + T4 plugin 2.0.7 + t4_blank_tpl_1.1.3
There is an error Undefined constant "T4\Helper\T4PATH_LOCAL"
Before install T4 Joomla is working fine. I've searched a forums. I checked file T4.php https://www.joomlart.com/forums/d/35321-warning-use-of-undefined-constant/14 Switching back to templates Protostar or Beez3 doesn't help. Even installation T3 and Purity theme not help, stiil message 0 - Undefined constant "T4\Helper\T4PATH_LOCAL"
Crazy :-)
PHP 8.0.11 | MySQLi 10.3.31-MariaDB-cll-lve