So I’m access Nextcloud via the domain that I’m pointing to the servers public IP address.
Hm, that’s not fully answering my question. If you’re on your LAN and trying to access your server using its domain name which is assigned to the “external” ip address, it most likely will fail because on your LAN the ip address is different and routing to the internet and back most lilkely doesn’t work.
I prefer to have a DNS server installed on my LAN which resolves the Nextcloud domain name to your internal address. See e.g.