PHP 8.4 changed exit and die to functions, so this call has no effect. Instead you can redefine those functions to do nothing.

<?php
function allow_exit( bool $allow ) {
  if ( PHP_VERSION_ID < 80400 ) {
    uopz_allow_exit( $allow );
  } elseif ( $allow ) {
    uopz_unset_return( 'exit' );
    uopz_unset_return( 'die' );
  } else {
    uopz_set_return('exit', static function() {});
    uopz_set_return('die', static function() {});
  }
}
?>

Test:
<?php
echo "Calling die() with allow_exit(false)\n";
allow_exit( false );
die();
echo "Calling die() with allow_exit(true)\n";
allow_exit( true );
die();
echo "Unreachable\n";
?>
Calling die() with allow_exit(false)
Calling die() with allow_exit(true)