You buy a domain from a domain registrar, like Cloudflare. You provide your public IP address to Cloudflare and when you use your domain name it will direct the request to your public IP.
If you don't want to pay for a domain name, there are free services like duckdns that will give you semi-custom domain names.
Jellyfin 10.10.3 (Docker)
Ubuntu 24.04 LTS
Intel i3 12100
Intel Arc A380
OS drive - SK Hynix P41 1TB
Storage
3x WD Red Pro 6TB CMR in RAIDZ1 (JF Library)