Making Nexcloud accessible over HTTPS with certificate

[Artichoke]

I mainly need Nextcloud to be accessible over HTTPS with a certificate so I can access my files from school. If the connection is not HTTPS or is HTTPS but with a self-signed certificate, the firewall blocks it. Also, obviously, HTTPS with a certificate is always the safest option in all scenarios. It looks like I'm not getting much of a response to this question, maybe I should post it on Let's Encrypt forums?