I don’t have iOS but you can see trending hashtags on the web so maybe there’s an equivalent on the app? You could also see all the latest post from you server and the entire Mastodon.
The best way to diversify the timeline for me is to directly follow tags of things you like.
No, you read it right. It’s kinda awkward to me as well, but I think it means that the opening is limited, like you can’t completely open the window beyond just a crack, to curb littering.