There's a lot of confusion and FUD going around on what is and isn't trained on when you use ChatGPT.
If you use ChatGPT's consumer interface (chat.openai.com), you are opted IN for your prompts being used to train/improve the service. There's a form you can fill out to opt OUT. (it's literally a Google form, which seems kinda janky, but it's pretty easy to opt out).
If you use OpenAI's API interface (api.openai.com), you are opted OUT for your input OR output data being used for training/improvement. There's a form you can use to opt IN.