No, routing is the flow of packets and is based on the static and policy based routes (policy does not mean firewall policies, thats a different entity) defined on the firewall.
The FIREWALL policies (I call them rules to make it easier) are the allow/deny/encrypt rules which determines which traffic is allowed to pass and whether to scan it or NAT it.
With NAT, generally, the rule of thumb is, all outbound (INT -> WAN) rules have NAT enabled, everything else doesn' t (ie INT->DMZ, WAN->INT, WAN->DMZ)
When a connection comes into an interface, first it is checked to see whether its allowed (via the rules), if it is, then it will them be scanned or natted as required and then routed to where it matches based on first checking the PBR, and then the static routes if no PBR exists.
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