This happens to non-native English speakers a lot (like me). My style of writing is heavily influenced by everything I read. And since I also do research using LLMs, I'll probably sound more and more as an AI as well, just by reading its responses constantly.
I just don't know what's supposed to be natural writing anymore. It's not in the books, disappears from the internet, what's left? Some old blogs for now maybe.
Books definitely have natural writing, read more fiction! I recommend Children of Time by Adrian Tchaikovsky
The wave of LLM-style writing taking over the internet is definitely a bit scary. Feels like a similar problem to GenAI code/style eventually dominating the data that LLMs are trained on.
But luckily there's a large body of well written books/blogs/talks/speeches out there. Also anecdotally, I feel like a lot of the "bad writing" I see online these days is usually in the tech sphere.