In case anyone runs into similar issues. Here is what worked, as suggested by ItsMePN.
If your site is on a loadbalancer such as CloudFlare, is_ssl() doesn’t work.
Neither did it work for me on a site hosted on “Cloudways + Digital Ocean”
Here is the gist https://gist.github.com/webaware/4688802 for force-ssl-url-scheme.php you need to download & upload it under wp-content/plugins & activate it.
Worked perfectly.