Also anything you don't say or do, given the anecdote. Which is just as relevant; without a well protected right to privacy against law enforcement, an unfounded claim is just as valid as a founded one, since there isn't any vetting. -Hopefully- there will be if a case is ever prosecuted, but there's a lot police can do to you to make your life miserable without requiring criminal prosecution and the burden on evidence that that entails.

Anything you say can and will be used against you in a court of law.

They’re explicit in saying how they will use information.

But that's only true after they read you the Miranda rights. Officers need to say those words so that the accused understands that their statements will be taken seriously in the immediate future.

It's not supposed to refer to anything that you have ever or will ever say in perpetuity...

That statement is the Miranda warning and refers to statements made during custodial interrogation. But yes, it does feel eerily true in general now.

It's also true of statements made prior to custodial interrogation, it's just that the police don't have to read you your Miranda warning prior to taking you into custody.

This means that you have to be super careful when speaking to the police at all. And by super careful I meant: don't. Watch professor James Duane's videos on the topic, and Don't Talk to Police. Also, if arrested, you can't just stay quiet: since Salinas v. Texas the defendant must actually invoke their 5th amendment right to keep quiet before actually keeping quiet, otherwise their keeping quiet... can be used against them in a court of law. You'll learn that from watching professor Duane's videos.