When the error in composer/platform_check.php is reached, we call:

trigger_error('…', E_USER_ERROR);

This is deprecated in PHP 8.4.

https://wiki.php.net/rfc/deprecations_php_8_4#deprecate_passing_e_user_error_to_trigger_error
https://www.php.net/manual/en/errorfunc.constants.php#constant.e-user-error

I expect this to throw new Error instead (which is similarly de-facto fatal, in that it uses Throwable, which is outside the Exception tree and thus is not likely caught by accident).

Or, perhaps back to echo + exit(1) like it was prior to #9414.