I've been working on enabling SSL for this website. In order not to overuse my brain on a Sunday, I followed the instructions of a DigitalOcean post (they are so useful, I highly recommend checking them out).
The post make you use Let's encrypt with Certbot. In a few commands, all is ready. It almost felt like knowing what SSL certificates were and how they worked was not needed. A big applause to the community who created both of them. Certbot directly modify your Nginx file so you just have to check that it's alright.
One thing I had overlook when first setting the site was the firewall ufw,
I first had to configure it to accept both HTTP and HTTPS to Nginx.
When I set HTTP redirection to HTTPS, the firewall was blocking HTTPS,
making the site unreachable (hopefully no critical system depend on it :) ).
Once I figured that, all went smoothly.
I'm looking at how to enable comments in a Hugo website (that is static). For the moment, I think I'll go with Isso, it's open-source, require no third-party and come 'battery-included'.