LLMs in theory can absorb a stream of integers into a pattern of weighted nodes. Every program written is vulnerable of being generalized into an LLM pattern. The outputs of AI and the predictive abilities, are not scary. The input capacity of AI will eventually eat every programmer's lunch and their programs too. The existential risk is mapping out computer programming as an entire field and locking it away.
If you really think that the job of programmers is at risk because the current wave of AI can write any program, that also means that AI can now write a new generation of AI systems that is potentially much more powerful than the previous generation and presumably this iteration process can proceed N times until the end result is sufficiently incomprehensible for humans.
Eventually such systems will work very well and be very useful and we'll rely on it more and more.
At that point the people worried about existential risk will point out that when a vastly superior intelligence is tasked to love and protect us, a lower intelligence, it may do things for 'our own good' that we may find appealing.
I'm just about to neuter my cat today