Thereās probably someone who can give you a better more specific answer, Iām not super savvy with snap packages but I would start looking at the documentation for the snap package
Check the āIncluded CLI utilitiesā -section
Basically If you have a domain name pointing to your nextcloud server/computer I would assume that you can install certbot (for setting up letās encrypt) and enable it for the domain you have set up nextcloud with. Certbot will assume that nextcloud is installed on port 80 and 443.
It also seems like thereās a utility included with the snap, try.
āsudo nextcloud.enable-https -hā for more info, you might be able to set it to use letseencrypt through that command.
Seems like the certificates are stored somewhere around here:
/var/snap/nextcloud/current/
You also should be able to symlink the certificates to the letās encrypt certificates which should be located here /etc/letsencrypt/live/domainname.com after youāve installed and deployed the certificates through certbot.