Apple One and iCloud subscription - What happens if I cancel my iCloud subscription

I have had the 2TB iCloud subscription for years. I just joined the Apple One trial. Now when I look at subscriptions my existing Apple News and Apple TV+ subscriptions show they will not be billed for both once the trial on Apple One ends and starts billing me. However, when I look at my iCloud account it now shows I have 4TB. I see that Apple is allowing you to add onto the Apple One iCloud so this appears intentional. You can actually now have up to 4TB of iCloud storage. That I have not seen documented by any reviewers yet.

However, I am only using about 1TB between all my family members. So 4TB seems overkill. What happens to my data if I cancel the original iCloud subscription? And should I wait until after the Apple One trial ends and I am actually paying before canceling the iCloud subscription. I am guessing that this would be no different than upgrading from the standard iCloud free plan to a larger one, not using the extra space, and going back to the free plan. But I don't want to lose almost a terabyte of data by accident.