When going to Room settings as an admin, some sections have forms without an "apply" button. When you make changes to forms in these sections, the changes are made live as soon as you modify the form. I realised this when I went to the Security tab: any change to Message history visibility are immediate. While exploring the app, I unintentionally changed the message history settings for a room I help admin, and didn't realise it until later.

This mode is mobile friendly and is practical for less critical things, such as managing a user's preferences, but for admin-level tasks I think it makes more sense to have an explicit button or some pop-up confirmation to apply changes.