Not required, but I have found it easy to do and easier to access your server from outside you home network. I use a domain along with a dynamic IP service. Plus I can use sub-domains for other self-hosted applications that I want to access outside my home network. Recently I added nginx proxy manager to manage all the inbound traffic to the various servers and sub-domains.

From the Nextcloud AIO GIthub page:

"Can I use an ip-address for Nextcloud instead of a domain?

No and it will not be added. If you only want to run it locally, you may have a look at the following documentation: local-instance.md"

I have a dyn account and it works for me. No hosting at all. That said, its price has gone up a lot since I first got it. My ISP rarely changes my IP on me, so I could probably get away with no hosting at all and just use my IP address as the nextcloud, but I didn't know that back when I started using it.

If you just want to access it with your own devices from anywhere, check out tailscale. I'm using it to access my desktop from anywhere and it works perfectly without having to screw around with DDNS.