You can just create a new passkey on the device from the new provider and register it with whatever service you are using. You can have multiple keys registered

You can just create a new passkey on the device from the new provider and register it with whatever service you are using. You can have multiple keys registered for a single service, like one unique key per device. In this case, you can use a non-google key manager such as this 1password password manager to manage your keys. Even when using a Google related app, your key is still on your device, it just won't be synced to your google account anymore in the case that google terminates your account.