From the Spaces Explore Rooms, I'd like to apply a filter to see spaces and rooms I'm *not* joined to

### Your use case

#### What would you like to do?

A button or filter or something to be able to see the rooms and spaces I haven't yet joined, including in subspaces.

#### Why would you like to do it?

To see what's changed, and to ensure my backup 2nd account is in all the rooms it's supposed to be.

#### How would you like to achieve it?

See above.

### Have you considered any alternatives?

Writing a script, but that's not as fun as using Element directly :)

### Additional context

_No response_