Dynamic Domain Name Service (Dynamic DNS or DDNS) is a service used to map a domain name to the dynamic IP address of a network device.
Yeah, you got one part of it in place, the DDNS, so remote clients can connect to the WAN IP of your Brume 2 should/when said WAN IP ever change. Now you need to 'get into' your LAN. The most secure way is to do that with a VPN. CGNAT on the IPv4 precludes you from using a straightforward 'WireGuard Server' or OpenVPN setup as opening ports on the Burme 2 will still be blocked upstream by your ISP. Unfortunately GL.iNet doesn't have full support for IPv6 (see GL GUI -> System -> Network). You'll have to go with an 'overlay'/'software defined network' VPN technology like ZeroTeir or TailScale. The latter is easier to set up on a GL device but the binary on 'em isn't up to date. See below for a possible solution.