The recent system update named High Sierra from Apple Inc. encrypted my entire disk and resulted in data loss. They didn't inform me that the update would encrypt the entire disk and that there was a risk that it may fail; it did fail, and my data is lost. Is there a way to sue Apple?
By clicking "accept" on the software license, you waived your rights to sue for damages. But you can go to the support forums and make an issue of what happened; Apple - like most companies - doesn't like bad PR. Official Apple Support Communities
Almost surely not. The waivers and disclaimers of liability associated with software from a company like Apple Inc. almost surely insulate them from legal liability. At most you might get a refund of the cost of the system update, but that was probably free.