Depends on the definition and your threat model but to make a very large story short; it’s email, others have copies (your gmail friends?). Metadata is public by default the body can be encrypted and encrypted at rest (comes with many limitations) and that’s the highest level of security you can realistically achieve.

If that works fine if not, use another method of comm. Email wasn’t designed to be secure.

Thank you. Sure. In Europe the "euro stack" approach becomes more and more relevant. So, the issue is more a compliance topic in the way of making use of service provides, who are best-case "eu-headquartered", but at least with a guarantee that processing on my side stays within the european realm. Doesn't mean very little in a technical understanding of security, I agree.