Dyndns on router DHCP mode

I have a DSL modem provided by my internet provider...behind this modem I have a Linksys router with openwrt in DHCP mode (Exposed mode on the DSL modem)...on the openwrt router are connected all the devices...I need to access these devices when I'm away from home...how can I configure the dyndns service?

The dyndns service will not allow access to the local devices, it will only allow you to reach the external IP address by name, even if you have a dynamic IP address; there is a guide about dyndns at https://openwrt.org/docs/guide-user/services/ddns/client.

To reach the local devices, you will also need some form of VPN, such as OpenVPN (https://openwrt.org/docs/guide-user/services/vpn/openvpn/basic) or wireguard.