Confidential Mode will push users further into Google’s own walled garden while giving them what we believe are misleading assurances of privacy and security.
It’s important to note at the outset that because Confidential Mode emails are not end-to-end encrypted, Google can see the contents of your messages and has the technical capability to store them indefinitely. In other words, Confidential Mode provides zero confidentiality with regard to Google.
https://www.eff.org/deeplinks/2018/07/between-you-me-and-google-problems-gmails-confidential-mode