Topic on Extension talk:Math

$wgMathValidModes does not forbid user or server to use the excluded options. I tested only on Mediawiki 1.35.1. For example, the below LocalSettings.php allows user to use 'source' or 'png':

wfLoadExtension( 'Math' );
$wgMathValidModes[] = 'mathml';
$wgDefaultUserOptions['math'] = 'mathml';

Same here. 1.35.x appears to ignore the settings to the configuration parameter.