NetBSD's native web server is called bozotic-httpd.
That small piece of software is dead easy to configure and is perfect to serve files over the web. So, assuming you got an authoritative certificate from Let's Encrypt using security/py-certbot, all you need to do in order to set up your server, is adding something like:
httpd_flags="-b -H -X -Z /usr/pkg/etc/letsencrypt/live/<mydomain.net>/fullchain.pem /usr/pkg/etc/letsencrypt/live/<mydomain.net>/privkey.pem -z ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-CHACHA20-POLY1305:ECDHE-RSA-CHACHA20-POLY1305:ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES256-SHA384:ECDHE-RSA-AES256-SHA384:ECDHE-ECDSA-AES128-SHA256:ECDHE-RSA-AES128-SHA256"
to your /etc/rc.conf.
-b: daemon mode, detach from console
-H: treat files starting with a period as hidden files
-X: enables directory indexing; this is if you only want to serve files and omit creating a index.html file on your server dir (by default /var/www)
-Z: cert and private key paths
-z: list of acceptable SSL ciphers
Now all you need to do is put your files at /var/www and start the service. The default layout will look like that of https://cdn.netbsd.org/
Refer to httpd(8) for a more in-depth description.