According to an article I read this morning in the WSJ, you would have to upload about 30 matching images to iCloud, at which point it would be flagged for review, and even then only the flagged images would be shown to the reviewer. This strikes me as not a serious privacy risk.
If your concern was that they might at some future point change their policies and do something objectionable then you should not be using iCloud at all.
Article here: https://apple.news/AhVzAY--DT36Oz22W7taL9Q