How to remove TLSv1.0 / 1.1 and enable TLS 1.3 in Nginx …

Step 3: edit options-ssl-nginx.conf

If you use Certbot to generate or renew Let’s Encrypt certificates, you probably won’t find the ssl_protocols line, but the following “include” command:
include /etc/letsencrypt/options-ssl-nginx.conf; # managed by Certbot

Exit nano without saving ( Ctrl + X ) and edit the Let’s Encrypt shared SSL settings:
sudo nano /etc/letsencrypt/options-ssl-nginx.conf

This configuration file is short:

# This file contains important security parameters. If you modify this file
# manually, Certbot will be unable to automatically provide future security
# updates. Instead, Certbot will print and log an error message with a path to
# the up-to-date file that you will need to refer to when manually updating
# this file.

ssl_session_cache shared:le_nginx_SSL:1m;
ssl_session_timeout 1440m;

ssl_protocols TLSv1 TLSv1.1 TLSv1.2;
ssl_prefer_server_ciphers on;

ssl_ciphers "ECDHE-ECDSA-CHACHA20-POLY1305:ECDHE-RSA-CHACHA20-POLY1305:ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-GCM-SHA384:DHE-RSA-AES128-GCM-SHA256:DHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-AES128-SHA256:ECDHE-RSA-AES128-SHA256:ECDHE-ECDSA-AES128-SHA:ECDHE-RSA-AES256-SHA384:ECDHE-RSA-AES128-SHA:ECDHE-ECDSA-AES256-SHA384:ECDHE-ECDSA-AES256-SHA:ECDHE-RSA-AES256-SHA:DHE-RSA-AES128-SHA256:DHE-RSA-AES128-SHA:DHE-RSA-AES256-SHA256:DHE-RSA-AES256-SHA:ECDHE-ECDSA-DES-CBC3-SHA:ECDHE-RSA-DES-CBC3-SHA:EDH-RSA-DES-CBC3-SHA:AES128-GCM-SHA256:AES256-GCM-SHA384:AES128-SHA256:AES256-SHA256:AES128-SHA:AES256-SHA:DES-CBC3-SHA:!DSS";

Again, remove TLSv1 and TLSv1.1 in the following line and add TLSv1.3:
ssl_protocols TLSv1 TLSv1.1 TLSv1.2;

The line should look like this:
ssl_protocols TLSv1.2 TLSv1.3;

Test the configuration, reload Nginx and test your Website.
nginx -t
sudo service nginx reload

Did these changes affect Certbot / Let’s Encrypt certifications renewals?

Check if renewal works using:
sudo certbot renew --dry-run

However, this check may be insufficient in our case. Please BACKUP your website before forcing a cert renewal:
certbot renew --force-renewal

In my experience, there were no problems with Certbot after making TLS version changes.

2. Enable HTTP/2 in Nginx

This part is really easy. First check your Nginx version:
nginx -v

To run HTTP/2, you must use Nginx version 1.9.5 or later – which should be no problem on Ubuntu 18.04 and later releases. You websites should also use SSL/TLS encryption.

Edit the server block configuration, for example:
sudo nano /etc/nginx/sites-available/default
OR
sudo nano /etc/nginx/sites-available/example.com

Look for the following lines within the server { } block:

# SSL configuration
listen 443 ssl default_server;
listen [::]:443 ssl default_server;

If you use Certbot, these lines will probably be at the end of the file and look like this:

listen [::]:443 ssl ipv6only=on; # managed by Certbot
listen 443 ssl; # managed by Certbot

Simply add http2 after 443 ssl on both lines. In the second example (Certbot), it should now like like this:

listen [::]:443 ssl http2 ipv6only=on; # managed by Certbot
listen 443 ssl http2; # managed by Certbot

Save the file and exit nano ( Ctrl + O , ⏎ Enter , Ctrl + X ), test the Nginx configuration and reload Nginx:
nginx -t
sudo service nginx reload

Test if HTTP/2 is active

To test if HTTP/2 has been successfully enabled, you for example use KeyCDN’s (free) online tool:
KeyCDN HTTP/2 Test Tool

By the way, HTTP/3 is coming soon: it is currently being implemented in Nginx 1.17 and making its way to Chrome, Firefox and Cloudflare.