I trying to install war 3 from battle.net but i can’t because the button for installing is hidden for me. I have my old keys from classic games and they are visible in my account.
Go to the main blizzard site then navigate to your games and subscriptions under account settings.
Scroll to the bottom of that page, and you will see entries for Warcraft 3 if you have added it to your account. Once you run the installer, it will talk to the Battle.net app and begin installing the game. You’ll then have a play button.