After upgrading to PHP 8.4.1 some deprecations appear:

Implicitly marking parameter [...] as nullable is deprecated, the explicit nullable type must be used (info)
Failing scenarios: (type) (name) = null
Fix for PHP ^8.0: (type)|null (name) = null
Fix for PHP ^7.1: ?(type) (name) = null
Older PHP versions: remove the (type)

Constant Bugsnag\E_STRICT is deprecated (info)
It seems like the E_STRICT constant is now assumed to be in Bugsnag namespace.

Error disappears when adding next lines of code in src/ErrorTypes.php (but it's a dirty fix):

if (!defined('E_STRICT')) {
    define('E_STRICT', 2048);
}

I didn't discover other scenarios yet. If so, I will extend this issue.