The title says it all. I hadn't used Lightroom in a while, but in the past, it has been extremely useful when I wanted to change contrast, white balance, and other board parameters of a large batch of photos. All that needed to be does was to select all photos in the grid, open the panel, and select a setting. All photos would gradually be updated with this setting.
I just came back in today to run the same procedure on a new computer and downloaded the lastest version of Lighroom -- but this feature is no longer present. Selecting all photos and applying a setting confers that setting to only the viewport photo. All the other photos are untouched. A quick look through the latest documentation lists a "Settings > Sync" function, but there is no settings menu and no sync function. In fact, the interface has significantly degraded in quality and efficiency, on several fronts.
Adobe continues to fail with these successive updates that either completely modify existing functionality or make it unsable altogether. If I have missed something, please let me know -- but I doubt it. All the changes coming down to the Adobe suite of products in the last year show that management has changed and quality control has flown straight out the window. I continue to be unimpressed.
You've almost certainly downloaded the wrong version of Lightroom....there are 2 current versions available, there's Lightroom Classic (stores images on your local system), which is probably the version you have been previously using, and there's the version called simply Lightroom, which stores images in the cloud (and which also has the ability to batch edit, but done in a different way).