Did you shred it before? If not, they already have what you put in publicly, available publicly, and it's all saved on their end even if you shred all publicly available content.

Reddit got your thoughts and they will monetize them either selling the data to AI companies or just getting ad/personal data money from people reading your content and interacting with it on their website.

It sucks to admit but if you didn't shred your account reddit still profits off you publicly, and even if you did shred your account, they will profit off you in backrooms instead.