Wipe the WordPress admin dashboard and replace with your own custom template

custom-admin-dashboard.php

<?php
add_action(
	'all_admin_notices',
	function() {
		$screen = get_current_screen();
		if ( 'dashboard' === $screen->base ) {
			/* Your code goes here */
			ob_start();
		}
	},
	99999
);

add_action(
	'in_admin_footer',
	function() {
		$screen = get_current_screen();
		if ( 'dashboard' === $screen->base ) {
			ob_end_clean();
		}
	}
);