Imagine that your local local movie theatre showed everything from the latest Pixar hit to film pornography. A single ticket allows anyone--even children---to enter the front doors and then choose a theater room. Which one shows porn? That's not clear until the movie starts, but somebody is handing out candy for entering theater 9.
Discord is like that. Some servers are well-supervised and kid-friendly, and kids can even join private servers with only their friends. Some are full of the darkest extremes of humanity, and they all look alike from the outside. Many kids join Discord to talk to an approved group, which is no more risky than any other group chat.
There's nothing that tells a kid that Disney is playing theater 4. If they joined the wrong room, would your child leave or stay out of curiosity and fascination? Could they cope with what they saw?
If you wouldn't let them go to that theatre without you, don't let them use Discord without you.
However, you cannot see the exact content of your teenagers' conversations. Safety relies on teens' understanding of the world. Even if you talk to your kids about their activity and online friends, they may not mention much about a conversation they believe is harmless. Groomers and extortionists excel at making a kid think they truly are friends. Kids don't always know when something is dangerous until it's too late.
In March, a child was kidnapped, raped, and found locked in a shed after being groomed for months on Discord. Her story might have been different if her parents had more visibility of her conversations on Discord.
As for the new restrictions, it's great to see another platform taking children's wellbeing into mind. However, the changes don't make the app a good choice for minors, especially if they have not learned (or are not yet developmentally ready) to navigate complex and ambiguous spaces online and understand how to recover when something goes sideways.