Ambiguous message: "You attempted to join using a room ID without providing a list of servers to join through."

### Steps to reproduce

1. Create a room.
2. Leave the room.
3. Try to "Join the discussion" again from "Historical".

### Outcome

#### What did you expect?

A message telling me that the room doesn't exist / can't be found on the server.

#### What happened instead?

A message telling me something that confuses me:

> **Failed to join**
> You attempted to join using a room ID without providing a list of servers to join through. Room IDs are internal identifiers and cannot be used to join a room without additional information.
> If you know a room address, try joining through that instead.

#### Additional information

In the browser console I see

> `POST https://matrix-client.matrix.org/_matrix/client/r0/join/!NVfMslxkPhhjsSXnGH%3Amatrix.org 404`

Not sure if it's always been like that or only recently because maybe [forget_rooms_on_leave](https://matrix-org.github.io/synapse/latest/usage/configuration/config_documentation.html#forget_rooms_on_leave) has been enabled for matrix.org?

### Operating system

_No response_

### Browser information

_No response_

### URL for webapp

app.element.io

### Application version

_No response_

### Homeserver

matrix.org

### Will you send logs?

No