Anything a LLM says is not plagiarism.
Let me correct that for you. Everything an LLM or text generator writes can be plagiarism, depending on how you use it.
If there is a topic that I find interesting regarding something I don't know a lot about, I might read articles from what I believe to be reputable sources, and I might paraphrase information that I find across several sources in my post. That is essentially what a LLM does.
Acquiring knowledge by reading what others have said on a particular topic and then explaining or writing about it the way you remembered it is not plagiarism. If it was, most of the stuff we say about Bitcoin could be classified as plagiarism. A simple question, like explaining what Bitcoin is can't be answered without saying something that other people haven't already said in the past (most probably).
Plagiarism is often about intention. If you find a research on hardware wallets and make it sound like you made the research, it's plagiarism. You can't write about that on the forum by saying that you conducted the research, you talked with experts, you spent hours configuring and working with the devices, if it was someone else who did it.
I also was using the grammarly as a supportive measure to atleast straighten and make my grammar a little bit readable but the whole chaos with AI generated or correct post made me let go because it got to a particular period when I actually felt that even the use of grammarly could be classified as AI.
Grammarly doesn't generate text on its own. It corrects the grammar of existing text you feed into it. You should be fine using Grammarly. No one should get into trouble for doing extra work to make their posts better, especially if English isn't their first language. It would be unfair if the admins punished users for using Grammarly.