Why YSK: Because you may delete your account and find your comments and other content is restored and beyond your control.
DO NOT DELETE YOUR ACCOUNT YET.
Keep overwriting your comments over and over so they cannot just roll them back a single edit.
I prefer Power Delete Suite as it does not need authorization and just uses the website through your own browser. I will continue to overwrite my comments on repeat until the API changes.
Power Delete Suite has a built-in backup feature. You can use it to save an offline copy of all your posts and comments before either deleting or editing.
This will only cover around 3000ish posts that are directly viewable from your profile. It will not cover absolutely everything like the GDPR request will.