Yeah, Shizuku opens up a massive attack surface through ADB. ADB can do a lot to your device without you even realizing it in a lot of cases, and you’re basically giving ADB access to Shizuku itself and any apps that use it (which could be exploited) at all times, so its very risky. Its pretty dangerous and definitely best to avoid an app like this.
They’re mods of the proprietary Discord client, so yeah they don’t meet the criteria. But the mods themselves are open source which is nice.