The was a useful feature to AUTO STACK BY CAPTURE TIME in previous versions, but can't find it in the new version ! In the stacking menu there are just stack/unstack options ! Is this moved to other menus ?
@JohanElzenga is right. You installed Lightroom for Cloud which is a completely different app and not what we all know as Lightroom. Normal Lightroom is now called Lightroom Classic. What Adobe Calls Lightroom Desktop is a port of the iOS/Android version of Lightroom to Desktop operating systems. It stores all your images in the cloud and misses a lot of the features you might be used to having in Classic Lightroom such as auto stacking by capture time. Lightroom in the cloud is great for people who want to store all their images in the cloud, their libraries to look identical on all platforms and devices, but who only rarely print their images and rarely share to social media. For all others, you want Lightroom Classic.