story
You can opt out of ChatGPT using your conversations for future training, without disabling any features like convo history.
Either some browser plug-in like an adblock is hiding the button from you, or you're not noticing and clicking it (I'm guessing the former [1]).
For me, on iPhone, there's a black button with white text "Make a Privacy Request" which sort of hovers bottom centre of the page the way "Chat Live with Support!" buttons often hover.
Click on that button to get to this - https://privacy.openai.com/policies?modal=take-control - which allows you to either delete your account, or:
"I would like to: Step 1 of 2 Do not train on my content Ask us to stop training on your content"
They then tell you it applies to content going forward, not stuff already done. But that's the opt out that doesn't require losing ChatGPT conversation history.
[1] On iOS Safari with 1Blocker enabled, I could see the button without it being hidden as an annoyance or widget or whatever, however when I tried entering email for opting out to check it still works it gave me an error message that suggested adblock type things might be the issue. I opened the page in Firefox for iOS (so same browser engine as Safari, but without 1Block) and it worked with no error message.
Roark66 gave a better answer, but...
On desktop I clicked the link and immediately saw "Make A Privacy Request" top right (where login / account / menu buttons might be)
I must ask did you honestly just miss this UI element or do you think it might be some confirmation bias that you already had?