Dynamic DNS on router with dynamic IP WAN address

I am investigating the use of NextDNS to protect all DNS requests on our internal network. We have a dynamic IP address on the WAN side of our router/firewall and are considering using NextDNS as follows. Create a NextDNS account. On the firewall, create a outbound NAT rule that maps port 53 to the DNS server address at NextDNS. Therefore, every DNS request coming from a system on our internal network would be routed to NextDNS no matter what destination IP address the system uses for DNS service. However, since our WAN ip address is allocated dynamically, I don't know how to inform the NextDNS server that our WAN ip address has changed (I assume the NextDNS server uses the source IP address to select the profile to use when filtering DNS requests). Note that no host on the internal network would be aware it is using NextDNS.

Is there a way to setup the profile such that we specify a DDNS domain name that will map to the dynamic IP address and therefore the appropriate profile will be used? Is there some other way to accommodate the dynamic IP addresses?