Ya got three options.

Option A is to create your own certificate that is self-signed. You will then have to load the certificate into any client you want to use. Easier than people realize, just a couple terminal commands. Give this a go if you want to learn how they work.

Option B is to generate a certificate with Let's Encrypt via an application like certbot. I suggest you use a DNS challenge to create a wildcard certificate.

Option C is to buy a certificate from your DNS provider aka something like cloudflare.

IMO the best is Option B. Takes a bit to figure it out but its free and rotates automatically which I like.

I like helping and fixing stuff, if you'd like to know anything just ask :D

Kleopatra

There are a few security issues with it, but all of the worst known issues require a valid login token. So an attacker would already need to have valid login credentials before they could actually do anything bad. Things like being able to stream video without authentication (but it requires already having a list of the stored media on the server, which means you have been logged in before). Or being able to change other users’ settings (but it requires already being logged in to a valid user).

Basically, make sure you use good passwords, and actually trust any other users to do the same.

You really shouldn't expose anything directly to the internet. It is a security problem waiting to happen. (Assuming it hasn't already)

This is how giant botnets form.

Nothing. People fearmonger