The sparkle icon is what you click/tap to change what tweets you see first. Your timeline can either show the top tweets or the most recent tweets. Why they chose sparkles to represent this is unclear to me.
By default, you see the top tweets. But if you switch to seeing the most recent ones first, the icon doesn’t change. So unless you remember the last time you switched, you can never really be sure which version of the timeline you’re viewing.
If you’re viewing the most recent tweets first, make the icon a clock. Something like, I don’t know, the very clock that Twitter uses if you click on the magic sparkles when your timeline is set to most recent first.