I manage several sites that use T4 blank template, and which were broken with a fatal error after the upgrade from 4.4.0 to 5.0.0.
The reason was a null parameter passed to a function expecting a valid array, see Joomla GitHub issue 42195, which was closed with a comment that the cause was in the T4 blank template code.
The following patch seems to fix the issue by passing an empty array instead of null:
--- administrator/cache/t4core/ModuleHelper.php.orig 2023-10-22 12:19:29.561364295 +0200
+++ administrator/cache/t4core/ModuleHelper.php 2023-10-22 12:18:03.126294747 +0200
@@ -364,7 +364,7 @@
$app = Factory::getApplication();
- $modules = null;
+ $modules = ;