Hide directories from wp file editor

functions.php

<?php

// Hide 'assets' directory from theme file editor.
add_filter( 'theme_scandir_exclusions', static function ( array $exclusions ): array {
	global $current_screen;

	if ( ! $current_screen || ! in_array( $current_screen->id, [ 'theme-editor-network', 'theme-editor' ] ) ) {
		return $exclusions;
	}

	$exclusions[] = 'assets';

	return $exclusions;
} );

// Hide 'assets' directory from plugin file editor.
add_filter( 'plugin_files_exclusions', static function ( array $exclusions ): array {
	global $current_screen;

	if ( ! $current_screen || ! in_array( $current_screen->id, [ 'plugin-editor-network', 'plugin-editor' ] ) ) {
		return $exclusions;
	}

	$exclusions[] = 'assets';

	return $exclusions;
} );