Why would FSD make the premium lower?
Insurers pay for crashes. FSD (Supervised) is on for those kilometres, with you still legally driving.
The remaining crashes should also be less severe. Severity is what blows up a premium.
Tesla Insurance in some US states prices FSD miles cheaper, up to 10% on some coverages. That figure is Tesla's. Zurich in Australia has started asking. Nobody sells that here yet.