I feel like this depressive kind of nihilism happens as a reaction to most of our culture being spun around higher meanings.
Whether that's religion, spirituality, some ridiculous Hollywood love story or pseudo-scientific universe theories.

Growing up in this context, many will discover that each of these higher meanings don't apply to them, because they don't believe in gods or spirituality, they don't have a Hollywood love story and those universe theories don't click with them either.
The obvious conclusion is depression. It appears to be required to have a higher meaning to lead a 'meaningful' life and you don't have one.

It's one hell of another mental leap to recognize that:

• those universe theories are pseudo-scientific bullshit.
• no one has Hollywood love stories.
• not believing in gods or spirituality also necessarily means you believe everyone else made them up. Which is a discouraged thought, due to tolerance, but needed here.

Equipped with all that, you're able to realize that no one has a higher meaning. It is not required. Nothing matters, but this fact does not either matter. And then you're free to choose your own non-depressive adventure.

I'm trying to be a nice, chill, helpful nihilist. I volunteer, I go out of my way to help.... and it's all just a front for the certainty that we can't 'stop at 1.5c' because that opportunity is long gone. my kid might get our stuff, but lot of good it'll do them in a world on fire. I keep it to myself as much as possible and try to project kindness and calm.

I think this is the preferable alternative to becoming convinced there were few / no downsides to me acting on my beliefs and potentially lashing out at the fossil fuel lobby, the rich, hypocrite politicians etc. so. And I'm certain I'm not alone there.