Silence deprecated notices?

Yep this is possible, docs are here: https://querymonitor.com/blog/2018/07/silencing-errors-from-plugins-and-themes/ .

To do this for WordPress core, use this code:

add_filter( 'qm/collect/php_error_levels', function( $levels ) {
	// Hide deprecated notices from core:
	$levels['core']['core'] = ( E_ALL & ~E_DEPRECATED );
	return $levels;
} );