For some reason Samsung has made the default resolution on the Galaxy S7 and S7 Edge display 1080p Full HD as part of the Android Nougat update. This is likely meant to be a battery saving and performance enhancing change. If you want to continue to take full advantage of your Galaxy S7's QHD display you still can, you just have to re-enable it in your display settings. To be honest you likely won't notice the difference now that you have received the update. If you just wan't to get the most out of the hardware you paid for head to Settings and then Display from there you will be able to toggle QHD back on.