Good for you, but let me tell you that a tool powered by AI is different than a LLM (large language model), which can be used to generate or manipulate texts or responses, and Grammarly is an AI-powered tool that helps you have more accuracy in your writing. As said by @Ultegra134, it has multiple functions and features, and it depends on the user which features they want to use, especially when posting in this forum, so that their posts aren't detected as written by an AI model, and that usually happens when you accept the suggestions it provides, in which case, it changes the whole sentences or paragraphs and then it might get detected as an AI-generated text.

English is not my first language as well, so I've also been using Grammarly for months now, not only for this forum but also because it's useful in writing content in general, and, I've never faced any problems with it because I only use it to correct what's wrong and don't take its suggestions when I know what I've written is correct because my English is good, it's just not perfect.