It's complicated, but the 2013-2014 years were when the bulk of the Snowden leaks were hitting the internet, and people were starting to dig up really suspicious stuff relating to all big tech companies, not just Apple. However, Apple was still among the companies compliant with PRISM, the NSA's newly established surveillance/tracking effort that also roped in Microsoft, Google, AOL and any other major service provider you can think of.

The implications of this are unclear. I like blowing these claims out of proportion, but in reality we genuinely have no idea what this means. It could simply signal that Apple is complicit with benign cloud-storage security procedures enforced by the USA. It could also mean that the US has carte-blanche access to iCloud data and decryption keys. You're free to draw your own conclusions, but the surrounding context seems to imply that Apple has an under-the-table relationship with our government (as does most of the tech industry, surprise surprise).

Oh, and I don't really know/care if LS is harmful. You should be aware that it's not going to outsmart Apple if they want to collect your info, though. They have kernel-level networking access, which companies like Microsoft have abused in the past to collect telemetry on crafty users. It's probably not harmful, per-se, but your perception of it as an impassible wall might be.

LS is not the only solution that I use. But is a good start and limits the telemetry baked into the macOS significantly. On my Debian installs, I use Open Snitch. https://bit.ly/3t6VSCk

Why do you trust Little Snitch? It's closed source and in the perfect position to steal information.

If worrying about closed-source threat models is something you spend a significant portion of your time doing, you shouldn't be using MacOS in the first place.