Man, gboard does that on android so much that I wound up installing and using heliboard. It kinda sucks but at least it doesn't "fix" your message after you type everything

It predicts what you are going to type as you type. It has a tendency to add words to the end of a message when you hit send.

Whatever it is, it's bad on GBoard, too, if you possess better than a 6th grade vocabulary.

This is actually a necessary feature for a touchscreen keyboard to feel usable, and it's been in iOS since day one. The problem is that it has gotten not only much worse over time at predicting which tap zones to enlarge, but it also feels more aggressive. For example, tapping the shift button on the iOS keyboard enlarges the Enter/Return key's touch area so much that I am unable to immediately tap the microphone icon to turn off dictation. If I've tapped shift, I need to then wait a second for the predictively-enlarged tap zone to shrink before I can turn off dictation.