Try this and see if it fixes your issue.
- Open Terminal, found in /Applications/Utilities/.
- Type the following line (or copy it and paste it) into the Terminal window, then press Enter.
defaults write com.blizzard.worldofwarcraft disable-expose-fix -bool YES
3) Quit Terminal. You should now be able to play properly.
This is the most common fix for modifier keys not working in macOS.