It sounds like you don’t know that you can turn off iCloud backups. I’ve never used it and backup locally. You’d also want to avoid using iCloud mail, photos, drive. Not sure what else, but if you want to avoid everything just in case, more power to you.
But not using end-to-end encrypted HomeKit with a few incidental devices that don’t show any patterns and don’t store data because you haven’t turned off iCloud Backups is an interesting line in the sand to draw.