This is a more recent problem in fandom, with the invention of AI bots like ChatGPT that can write stories. If you want to use AI for your writing, it is not my place to stop you, but I am going to be blunt: most people in fandom do not like AI writing at all. Almost everywhere I go it's viewed very negatively, and most commonly considered art theft, due to the writing used to train the AI bots not being used with permission. A common feeling I see is "If you don't care enough to take the time to write something, why should I care enough to take the time to read it?" It is viewed as disingenuous, and like you've deceived people by offering something presented as coming from a place of love and passion, but it's actually not those things.
I understand that all sounds very negative, but if you want to use AI to write your fanfiction, I am not going to tell you point blank not to. You should, however, be aware of the larger feelings surrounding it and the way people will likely view what you post. That is all I will say on the matter, I will leave the rest up to you.