Very short videos in Instagram are called reels. Just like tiktok videos. The button looks like this and are videos only. Would be very cool to implement, would attract younger people, definitely. 
https://m.primal.net/MdWN.jpg 

 In the search button, you you click on it, you get the feed with photo posts and the search button in top of the window.  

 So you basically have the search and feed button in one window, and a button for shot videos named reels.  

 The search button contains the also topics.