I mean, genuine question, is Linux Mint or MX Linux endangered by this?

Unless I'm missing something, I have zero concern for companies who sell out by complying.

The code was "free as in freedom" when you decided to build your company on it; and while you're not legally obligated to defend that freedom, and I, and hopefully other consumers, find that you are morally obligated to.

I think this is the way that Linux desktop distributions are endangered, quoting from the article: "... apps and websites will not assume liability when a signal is not provided and assume the lowest age bracket. Any Linux distribution that does not provide an age bracket signal will result in a nerfed internet for their users."

Not by the California law, since that law poses no danger.