This article provides information about the dynamic gateway for DHCP/PPPoE type interfaces.
To route both to be active with static route on the routing-table, enable the below option from the CLI:
First, set the interface to not get the Dynamic Gateway:
# config system interface
edit wan1 (or other port)
set role wan
set defaultgw disable
# config router static
set dynamic-gateway enable
Once enabled, dynamic-gateway hides the gateway variable for a dynamic interface, such as a DHCP or PPPoE interface.
When the interface connects or disconnects, the corresponding routing entries are updated to reflect the change.