In this example, the update is blocked for Akismet and Classic Editor, but it can be used with any plugin. Don’t do this unless you have no alternatives.

/**
 * Block some plugins from updating
 *
 * @param array $parsed_args
 * @param string $url
 *
 * @return array
 * @throws JsonException
 */
function wporg_block_update_specific_plugins( $parsed_args, $url ) {

	$blocked_plugins = [
		'akismet/akismet.php',
		'classic-editor/classic-editor.php',
	];

	if ( isset( $parsed_args['body']["plugins"] ) ) {
		$plugins = json_decode( $parsed_args['body']["plugins"], true );

		if ( isset( $plugins['plugins'] ) ) {
			$installed_plugins = $plugins['plugins'];

			foreach ( $blocked_plugins as $p ) {
				unset( $installed_plugins[ $p ] );
			}

			$parsed_args['body']['plugins'] = json_encode( [ 'plugins' => $installed_plugins ], JSON_THROW_ON_ERROR );
		}
	}

	return $parsed_args;
}

add_filter( 'http_request_args', 'wporg_block_update_specific_plugins', 5, 2 );