I don't know how to use this function without using the mouse. I find it annoying and want to get rid of it. I don't even know what it's called. When I look in help for predictive text I get info re auto correct'.
If the popups appear in other programs besides Word (such as a browser), it isn't a Word function but a Windows 10 feature. Go to Settings > Devices > Typing > Hardware Keyboard. If the "Show text suggestions as I type" feature is turned on, click to turn it off.