They could do it by not uploading any of the data, or if they do, uploading it encrypted with the only key being on the user's device or a passcode.
Both are well established ways to secure data, but the company itself would not be able to interact with the data at all past storing it, so any features/revenue there would end.
YouTube you can skip ads with uBlock origin for the normal kind and sponserblock for the embed "ad read" kind the youtuber does.