How do I set up a wildcard DNS for use in Cloudways with a Wordpress multi-site set up [ example mysite.domain.com ] ?

If your websites are going to remain within the subdomain system of "mysite.domain.com", it's a simple enough solution of checking off the Wildcard box for SSL when activating Let's Encrypt and ensure that * is set up in your domain's DNS settings. If your sites are going to be mapped with their own domains eventually, wildcard DNS doesn't quite work for multisite automatically. You'll have to manually add new domains to your SSL list as they're processed through WordPress. Luckily, you won't have to recreate that list each time a new WP site is created, you'll simply have to add the new domain (up to 99 I believe) to the list found in SSL settings.