Does the keyboard work as expected if you switch to a text console (eg. Ctrl+Alt+F2)?
Are you on the default stable branch?
If yes and yes, you can try reinstalling the libinput package, and make sure you don’t have any libinput package installed from AUR.
Another thing you can try is to check your Gnome third party extensions if you have any, there were some issues I saw mentioned because some extensions haven’t been updated to work with 45.