Default allow ICMP

Hi, and welcome to the forums. ICMP is in no way special compared to other IP traffic. If you want to allow it across interfaces then you have to explicitly allow it in the policy. To make life easier Fortinet gave us the service group object. If you add ICMP or PING to your custom service group that you use in every policy between VLANs then you' re done in a second.

If your VLANs will be setup in the same way requiring the same policies you could create a Zone. Add all of your interfaces into the Zone and create a policy of Zone to Zone ICMP allow. Intra-zone traffic is allowed by default.