I feel most of them are either dangerous (tide pod challenge)

You say most and then cite only the most overblown, ridiculous example. I haven't seen a single death actually linked to the tide pod challenge, it was just a meme that a select few idiots took too far and got hospitalized. That happens with literally any popular trend. Don't forget millennials had plenty of "dangerous" trends (planking, off the top of my head) that the mainstream media blew out of proportion.

illegal (property damage in your school bathrooms)

This has been happening to school bathrooms for a very long time, it just wasn't on social media prior. I remember a trend in my area of kids fucking up their school bathrooms.

absolutely tone-deaf (all those people pretending to have xyz disorder because it's quirky)

So millennials didn't do all sorts of incredibly tone-deaf impressions and jokes back in the day?

or just flat out dumb (think fortnite and such if that's still even a thing and the slang as well)

"Fortnite dumb" like okay. Fortnite isn't dumb, it's just not made for you. I don't enjoy it, but I love playing it with my nieces and nephews, and while again it's not my speed, it's definitely not dumb.

The slang they use feels like a foreign language and I refuse to learn it just like I did with a lot of slang from my time.

If you just hate using slang that doesn't mean gen z slang is dumb, just means ur a hipster.

There's plenty of totally enjoyable, innocent gen z trends as well as some obnoxious ones, gen z slang is just an evolution of millennial slang, and gen z are more savvy in some areas and less so in others than millennials. But ofc ppl are gonna see what they want.