My elementary school kid came home yesterday and showed me a piece of writing that he was really proud of. It seemed more sophisticated than his typical writing (like, for example, it used the word "sophisticated"). He can be precocious and reads a ton, though, so it was still plausible that he wrote it. I asked him some questions about the writing process to try to tease out what happened, and he said (seemingly credibly) that he hadn't copied it from anywhere or referenced anything. He also said he didn't use any AI tools. After further discussion, I found out that Google Docs Smart Compose (suggested-next-few-words feature) is enabled by default on his school-issued Chromebook, and he had been using it. The structure of the writing was all his, but he said he sometimes used the Smart Compose suggestions (and sometimes didn't). He liked a lot of the suggestions and pressed tab to accept them, which probably bumped up the word choice by several grade levels in some places.

So yeah, it can change the character of your writing, even if it's just relatively subtle nudges here or there.

edit: we suggested that he disable that feature to help him learn to write independently, and he happily agreed.