That’s not correct, someone with a bolt cutter can get any link in the chain and it causes collapse.

Single point of failure doesn’t mean “weakest link”. It means if this one piece (“single point”) fails, the whole system will fail.

Which is true, but also not what's being discussed, which is "single point of failures", not "weakest link".

But you don’t know which, and others may fail first due to various adverse events (say, random micrometeoroid strike). If any link fails, the whole chain fails.

Contrast a second chain, or double linked chain, so if any link fails the load is not lost.

This assumes the environment is completely predictable.

If you know the strength of every link in the chain with perfect accuracy, and you know that the only potential cause of failure is too much weight being placed on the chain, then the only link that can fail is the weakest[1] one because no other failure can happen before that one.

But really you need to design for the idea that various things might happen. Someone else gave the example of a person choosing a link to cut with bolt cutters. The person's choice is what's not predictable in that example.

---

[1] And if you assume it's not possible to have two links that are exactly as strong as each other.

"only one link is actually the weakest"

Which isn't relevant since (obviously) no one was talking about how many links are the weakest link.

"it is at that link where the chain will break"

Wars have been lost by thinking this way. e.g., D-Day was a successful assault on a strong link.