This isn't the same thing. This is a commanded recital of a lack of capability, not that its confidence in it's answer is low. For a type of question the GPT _could_ answer, most of the time it _will_ answer, regardless of accuracy

I just noticed that when I ask difficult technical questions, but for which there is an exact answer, he often tries to answer plausibly, but incorrectly instead of answering "I don't know".

Have you tried setting a custom instruction in settings? I find that setting helps, albeit with weaker impact than the prompt itself.

It's not a problem for me. It's good that I can detect chatGPT by this sign.

It doesn't become smarter except for releases of new models. It's an inference engine.

I read an article where they did a proper Turing test and it seems people recognize it was a machine answering because it made no writing errors and wrote perfectly

I've not read that, but I do remember hearing that the first human to fail the Turing test did so because they seemed to know far too much minutiae about Star Trek.