Google's software keyboard, aptly named Gboard, is a great product that a whole lot of people use every day. If you're one of them you might have noticed that you don't get a spelling suggestion when you're supposed to since the last update. If you haven't noticed and think your spelling really improved, I'm sorry to be the one to break it to you but it's just plain broken.
Since the tail end of January, folks have noticed the lack of suggestions or incorrect suggestions while using Gboard and devices from Samsung, Nokia, Huawei, Xiaomi, and Google's own Pixel line are well represented in the bug reports. We're seeing it ourselves, and some of us (OK, me in particular) really need help when it comes to typos.
An odd quirk is that you can connect a keyboard over Bluetooth or USB and things are back to normal but only while a keyboard is attached. This sounds like something Google is going to have to fix themselves, and let's hope they get on it — the problem's been around a while.
In the meantime, you can either roll back to an older version of Gboard — I uninstalled updates and the un-updated version in Android 8.1 for the Pixel 2 works fine — or try one of the many other great keyboards available in the Play Store.