Writing with LLM is also not writing. In some abstract sense, it may be plagiarism. In another sense, you're robbing yourself of one of the most crucial parts of writing: improved cognition. Anyone who edits voice transcripts knows just how much a normal person wanders, pauses, misspeaks, etc when talking. The act of writing forces you to refine thoughts you would not have otherwise had.
I find it interesting that you could technically apply the same to writing code: you're producing software, but without engaging your cognition fully. Sometimes, when the complexity of the project is too high, it might be okay, to not let you get sidetracked and distracted. But if you do that regularly, I feel like that ability will atrophy.