A simple example of using filemtime() to version enqueued assets with their last modified time. Snippets for https://hookturn.io/2021/10/automatic-versioning-strategy-for-enqueued-wordpress-assets/

functions.php

<?php

// A simple example of using filemtime() to version enqueued assets with their
// last modified time. 
add_action( 'wp_enqueue_scripts', function () {

	wp_register_style(
		'styles',
		get_stylesheet_directory_uri() . '/style.css',
		[],
		filemtime( get_stylesheet_directory() . '/style.css' )
	);
	
	wp_register_script(
		'scripts',
		get_stylesheet_directory_uri() . '/scripts.js',
		[],
		filemtime( get_stylesheet_directory() . '/scripts.js' )
	);

	wp_enqueue_style( 'styles' );
	wp_enqueue_script( 'scripts' );
} );

use-versions-when-enqueuing.php

<?php

// This example demonstrates how we can use wp_enqueue_style() and wp_enqueue_script() 
// functions directly to both register and enqueue the asset in one call. 
add_action( 'wp_enqueue_scripts', function () {

	wp_enqueue_style(
    		'styles',
		get_stylesheet_directory_uri() . '/style.css',
		[],
		filemtime( get_stylesheet_directory() . '/style.css' )
	);
	
	wp_enqueue_script(
		'scripts',
		get_stylesheet_directory_uri() . '/scripts.js',
		[],
		filemtime( get_stylesheet_directory() . '/scripts.js' )
	);
} );