you for reaching out on the community and telling us about your issue. I do
apologize for the issue you're having. Are you trying to shut down the Sync entirely? if so we should be able to do so by going across the top of Quicken and selecting edit > preferences > mobile & web > Sync off. From there the sync should be turned off. If you're trying to remove accounts you should be able to do so by going to the mobile and web tab. From there on the right it should have a list of all your accounts and a button as well that lets you adjust what accounts you want actively synced to the cloud.
let us know if this helps resolve the issue for you.