They sound like 90s grunge to me and I kinda love it. They also sound like teenagers, which is what they are (I think) so, there’s that. It’s like a mix of Hanson, Weezer, and Nirvana. It’s not bad, maybe not great, but what’s with all the hate/love/intergenerational controversy?
In a similar way that numetal emerged and combined existing popular genres, hyperpop is doing that now. 100 gecs sound like every genre of MySpace music fused al la The Fly. It’s a little bit of a meme, but some of it is so good.
Their last album was dedicated to using mostly actual instruments. So that’s where a lot of that grunge sound is from. But dig in, they rule.