block-plugin-update.php

<?php

add_filter('http_request_args', function( $r, $url ) {
	if ( 0 === strpos( $url, 'https://api.wordpress.org/plugins/update-check/1.1/' ) ) {

		$blocked_plugins = array(
			'plugin_name_1',
			'plugin_name_2',
			'plugin_name_3'
		);		
		if (!empty($blocked_plugins)){
			foreach ($blocked_plugins as $plugin){
				$plugins = json_decode($r['body']['plugins'], true);
				
				if (array_key_exists($plugin, $plugins['plugins'])){
					unset($plugins['plugins'][$plugin]);
				}
				
				$r['body']['plugins'] = json_encode( $plugins );
			}
		}
	}
	return $r;
  
},10, 2 );