When SD-WAN is enabled on FortiGate, the load balancing algorithm for Equal-Cost Multi-Path (ECMP) is configured using the load-balance-mode parameter under SD-WAN settings. However, if SD-WAN is disabled, the ECMP load balancing algorithm can be configured under config system settings. This flexibility allows FortiGate to control traffic routing behavior based on the network configuration and requirements.
Reference:
FortiOS 7.4.1 Administration Guide: ECMP Configuration

Enable NAT on the Allow_access firewall policy (A):
The Allow_access firewall policy must have NAT enabled to allow the webserver to use its VIP external IP address (10.200.1.10) as the source NAT when initiating traffic, such as pings, to the remote server.
Disable port forwarding on the VIP object (D):
Port forwarding is designed for specific port mapping, typically for services like HTTP or HTTPS. To use the VIP external IP as a source NAT, port forwarding should be disabled. Disabling port forwarding ensures that the full VIP IP address is used without being tied to specific ports.
Why other options are not correct:
B . Create a new firewall policy before Internet_Access for the webserver and apply the IP pool:
This is unnecessary as the VIP object itself is used for SNAT in this case, and an additional firewall policy is not required.
C . Disable NAT on the Internet_Access firewall policy:
Disabling NAT on this policy would prevent the NAT functionality needed for the webserver to use the VIP external IP address as the source IP.
Thus, enabling NAT on the Allow_access policy and disabling port forwarding on the VIP configuration are the valid steps to achieve the goal.

Both interfaces must have directly connected routes on the routing table In NAT mode, each interface must have a corresponding entry in the routing table, typically as a directly connected route, to route traffic between them effectively.
Both interfaces must have IP addresses assigned
In NAT mode, each interface must have an IP address to participate in routing and NAT operations. The IP addresses allow the FortiGate to forward traffic between different network segments.

Advanced mode allows for configuration as an LDAP client and supports group filtering directly on the FortiGate, as well as nested or inherited groups.

If the SD-WAN traffic logs do not show the specific SD-WAN rule name, it likely means that FortiGate is using the default or implicit SD-WAN rule to balance traffic. The implicit rule comes into effect when no explicit SD-WAN rule is matched, and as a result, the SD-WAN rule name is not displayed in the logs. The default behavior is to load balance the traffic across available interfaces based on SD-WAN strategy.