Fi has two different, incompatible options for how to sync your messages to a computer or other device that isn't your primary phone with your SIM (or e-SIM): the so-called "option 1" is RCS compatible, but treats your phone as the canonical device that has the primary copy of all messages, voicemails, etc. "Option 2" is device agnostic, where all messages and voicemails live on the cloud, and your phone (and all other devices) merely syncs with that primary copy in the cloud.

If your phone breaks or dies or is lost/stolen, Option 2 keeps chugging along with all your logged in devices, but the dead phone is the single point of failure for Option 1.

Ideally there would be a device agnostic way to access RCS through your account, but every implementation seems to require a specific SIM.