will i still have 200 GB after downgrading?

Also read the paragraph 'What happens when you downgrade or cancel iCloud+' in Downgrade or cancel your iCloud+ plan - Apple Support

and/or the related one at the bottom of this document Share iCloud+ with your family - Apple Support

It's not clear if or when Apple will actually get around to deleting files but your ability to do things such as backups will be curtailed until you delete files to whatever your lower or free plan allows. In other words you may find you still are using 200 GB for a while but Apple probably won't let you do anything except download and delete those files once you reach the end of your subscription date.

You'll have your existing amount of storage until the current billing cycle ends, and the amount you downgraded to after that.

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