If your Android phone’s keyboard is acting up after installing a third-party app from the Play Store or someplace else, there’s a chance that the app is messing up the normal functioning. To figure this out, you can boot the phone in Safe Mode and check whether the keyboard works. 

Press and hold the side button until the power options show up. 
Hold the power off option until the Reboot to Safe Mode option appears on the screen.
Once your phone starts, open the default messaging app and check if you can type easily.
If the issue doesn’t exist in Safe Mode, you should immediately consider deleting the third-party app you installed recently.
Should you fix the problem, well and good, but if it persists, you might have to switch to another keyboard. The Google Play Store has many input apps, but the most trusted ones include Swiftkey, Grammarly, and Google Keyboard. However, if the third-party keyboard apps don’t work on your phone as well, you’re probably left with limited workarounds. In such a scenario, visiting the authorized service center should be best. 

SlashGear
https://www.slashgear.com/1244996/android-phones-keyboard-how-to-fix/