How to disable preview updates

I'm sorry you're going through that and do feel for you as I have the same issue. I've reinstalled Windows 11 well over 15 times on my personal PC since December including a reformat of ssd's and reinstalling W11 using a usb media creation tool. USB seems to be the best way to ensure no registry rules are left behind. 

But regardless, W11 optional preview updates continue to install for me as well plus I am not enrolled in Windows Insider Program and have auto updates turned off. Even after re-installing Windows 11, I'll boot up my pc a few days later and find that W11 has re-installed all optional preview updates. It's insane that we don't even have control over our own PC's and W11 pretty much ignores and does the opposite of what you tell it. 

The only work around I've found is to keep updates paused. Problem is, once you unpause, W11 will eventually install the optional preview updates. I’m personally keeping updates paused permanently moving forward. I've been battling this since December. Good luck!