Spaces/rooms UI/UX structure is incredibly bad if the community needs many rooms (e.g. 25)

**Is your feature request related to a problem? Please describe.**
currently, if I need to have 25 rooms (channels) in my space, I have to make them all suggested rooms. Otherwise, the user has to click the "explore rooms" button to find them, which is a difficult button to find by itself. That's extremely bad UX. The user has to join each room individually. Then in the element app, he will see these rooms twice. One in section "rooms" because he joined them and one in "suggested" section. Then when I'll add a new room, he won't see that a new room has been added, because the "suggested" section will be overcrowded by the previous 25 rooms he already joined. Complete mess.

In my type of community, it's critical for users to see new rooms (channels). We used discord and it was great UI/UX until we got banned.

**Describe the solution you'd like**
Solutions require modifications of android app, ios app, web app.

easy fix: at least don't show a room in suggested rooms if the user has already joined that room. And place "suggested rooms" section above "rooms". If 0 suggested rooms, then don't show the section.

medium fix: make it possible for space admin to make it so that users who joined that space autojoin all rooms in that particular space. And most importantly, if a new room in space is created, everybody is joined to it automatically.

also, what's really missing is the capability to switch between rooms easier in the mobile app, like in the discord app all you need to do is swipe right and tap on the channel, very simple. On the current element mobile app, you need to tap on the channel, then swipe back, then tap again. E.g. on the swipeable left sidebar, where space can be selected, below space could be expandable list showing rooms in that space.

**Describe alternatives you've considered**
Looking at different chat platforms to host the 1.5k member community.

If at least "easy fix" could be implemented in ~2 days on android, ios, web, I could send 100$ to the dev doing that, because I need a solution to restart my community asap and it's a bit of a deal breaker if they will have trouble joining many rooms (channels) and will miss certain rooms (channels). In my case it's crucial for user to notice that a new room has been created.

The issue covers several possible room-discovery and navigation changes across Android, iOS, and web, but names no files, tests, or entry points. First narrow the request to one agreed behavior and client; done should be defined by that behavior working consistently and making newly created rooms discoverable.

Written by the indexing model from the issue text.