Someone linked linuxserver.io docker image that you can use with local IP. Then if you want nextcloud for yourself or just a few family members, you can setup VPN and still use local IP from anywhere. No need to buy a domain, but you need some (free) service like duckdns that tracks your public IP so you can connect to your home network anytime. You can also set your custom domain using reverse proxy (made up domain name for local use, still not payed one), but you will have to allow it in your nextcloud config
Buying domain and setting up certificates is what Im going to do just to get rid of cert warnings in a browser on my phone