Regarding flight feature/class "ProjEnableAddTaxToSalesPriceFlight" by default it was enabled in Tier 1 ( dev VM) and by default in was disabled in sandbox ( Tier2) machines.
when we verify enabled and disabled flight features from “SysFlighting” table. It was empty it means by default enabled. but when raise support request (TrackingID#2207070030001703) for more clarity we got update as "Yes, there is no record in ‘SysFlighting’ table because our engineering team confirmed the flight is handled by ECS kill switch, not by SysFlighting table." and also came to know that there is no place to see enabled and disabled flight details for customer.
we spent lot of man hours to debug why there is different behavior, until we reach out to MS we didn't get any idea on ECS kill switch. It strongly recommended that all flight feature enabled or disabled should be visible to customer.