Enable Duolingo Debug Menu and get Ambassador Preview Features
This is a powerful admin debug menu that gives you the ability to modify parts the site. I discovered this by looking through the webpack and saw that the role "admin" gives access to these tools (not sure why they dont obfuscate their webpack more). Anyways, it can do stuff such as editing the duolingo tree, hearts, disabling ads, disabling experiments, grade all answers correct, enable all questions on hard mode and much more. This has never been seen before on the desktop site by normal users or atleast I haven't seen it posted publiclly. With this debug information you can probably find more api endpoints in Duolingo which could be used for exploiting or for making something actually helpful like a duohardmode extension. If you add it to your script please give credit to me for finding it and making it usable for the general public.
Note: It is a settings icon on the very bottom right of the site.