It's not true adverts like we are used to. This is the blog post from last month:

Quests are a way for players to discover games and earn rewards for playing them on Discord. We started experimenting with them over the last year, and millions of you opted in and completed them. We’ve heard great feedback from developers who partnered with us to create them and from many of you who completed one. If you didn’t see firsthand, the "May the 4th" Fortnite Quest is a great example. Now, we’re opening up sponsored Quests to more game developers.

Quests will show up tastefully in Discord where you can opt-in to stream your game to friends and win rewards for playing. Some players will be made aware that a Quest is available, while others will discover it as their friends accept and embark on the Quest. Developers and publishers who sponsor Quests will work with our team to build an experience that showcases their game and offers a reward tailored for their game.

"tastefully", lol. That's for the users to decide.