PHP8: how to replace -autoload() with spl_autoload_register?

I am trying to use an older* WP install (4.8.17) with PHP 8.
I get this fatal error: __autoload() no longer supported, use spl_autoload_register() istead!

do you know if it would be difficult to repair this, without knowing PHP?
how should I rewrite that function with spl_autoload_register instead of _autoload?
thank you in advance!

the problematic line with the “autoload” function is in /wp-includes/compat.php and says:

	function __autoload( $classname ) {
		global $_wp_spl_autoloaders;
		foreach ( $_wp_spl_autoloaders as $autoloader ) {
			if ( ! is_callable( $autoloader ) ) {
				// Avoid the extra warning if the autoloader isn't callable.
				continue;
			}

			call_user_func( $autoloader, $classname );

			// If it has been autoloaded, stop processing.
			if ( class_exists( $classname, false ) ) {
				return;
			}
		}
	}

and here is the whole context:

// SPL can be disabled on PHP 5.2
if ( ! function_exists( 'spl_autoload_register' ) ):
	$_wp_spl_autoloaders = array();

	/**
	 * Autoloader compatibility callback.
	 *
	 * @since 4.6.0
	 *
	 * @param string $classname Class to attempt autoloading.
	 */
	function __autoload( $classname ) {
		global $_wp_spl_autoloaders;
		foreach ( $_wp_spl_autoloaders as $autoloader ) {
			if ( ! is_callable( $autoloader ) ) {
				// Avoid the extra warning if the autoloader isn't callable.
				continue;
			}

			call_user_func( $autoloader, $classname );

			// If it has been autoloaded, stop processing.
			if ( class_exists( $classname, false ) ) {
				return;
			}
		}
	}

	/**
	 * Registers a function to be autoloaded.
	 *
	 * @since 4.6.0
	 *
	 * @param callable $autoload_function The function to register.
	 * @param bool     $throw             Optional. Whether the function should throw an exception
	 *                                    if the function isn't callable. Default true.
	 * @param bool     $prepend           Whether the function should be prepended to the stack.
	 *                                    Default false.
	 */
	function spl_autoload_register( $autoload_function, $throw = true, $prepend = false ) {
		if ( $throw && ! is_callable( $autoload_function ) ) {
			// String not translated to match PHP core.
			throw new Exception( 'Function not callable' );
		}

		global $_wp_spl_autoloaders;

		// Don't allow multiple registration.
		if ( in_array( $autoload_function, $_wp_spl_autoloaders ) ) {
			return;
		}

		if ( $prepend ) {
			array_unshift( $_wp_spl_autoloaders, $autoload_function );
		} else {
			$_wp_spl_autoloaders[] = $autoload_function;
		}
	}

	/**
	 * Unregisters an autoloader function.
	 *
	 * @since 4.6.0
	 *
	 * @param callable $function The function to unregister.
	 * @return bool True if the function was unregistered, false if it could not be.
	 */
	function spl_autoload_unregister( $function ) {
		global $_wp_spl_autoloaders;
		foreach ( $_wp_spl_autoloaders as &$autoloader ) {
			if ( $autoloader === $function ) {
				unset( $autoloader );
				return true;
			}
		}

		return false;
	}

	/**
	 * Retrieves the registered autoloader functions.
	 *
	 * @since 4.6.0
	 *
	 * @return array List of autoloader functions.
	 */
	function spl_autoload_functions() {
		return $GLOBALS['_wp_spl_autoloaders'];
	}
endif;

(*The old WP is mandatory, as the theme is no more developed).

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