Macbookpro D-key board wont work on specific applications

I've recently got a Macbook Pro and everything works fine even the keys for the most part, however, I run into problems using the D key in a downloaded application ( Super Smash Flash 2). I've tried restarting my computer and even deleting the app and its files to reinstall them later and it still won't work. Any ideas on how to fix this? I've been at it for a few days now and the only thing I found was an old Apple community post from 2015 but that's way out of date, and it doesn't work anyway :(