SAML/SSO Obligatory Backup FAIL

### Steps to reproduce

Steps to reproduce

The matrix/synapse server needs to be serving the following json :
{"m.homeserver":{"base_url":""},"m.identity_server":{"base_url":"https://"},
"io.element.e2ee": { "secure_backup_required": true , "secure_backup_setup_methods": ["passphrase"]}}
Very first Login
Login for the first time --> you are not obliged to setup secure buckup (Unlike android and WebClient)

### Outcome

As served in the json the expected behavior is :
The user needs to be obliged to setup secure buckup before start chating (maybe after sending the first message as in the web 1.11.17 and android).
This is important configuration to avoid loosing the chat history.

### Your phone model

Iphone 13

### Operating system version

IOS

### Application version

1.9.15

### Homeserver

_No response_

### Will you send logs?

Yes

Reproduce the first-login flow on iOS with the reported server JSON, focusing on whether secure backup setup is enforced before the user starts chatting. Compare the behavior with the stated Android and WebClient behavior; done means setup is required when secure_backup_required is true.

Written by the indexing model from the issue text.