There is 1 open security issue in buster.
1 issue left for the package maintainer to handle:
GNOME Geary before 3.36.3 mishandles pinned TLS certificate verification for IMAP and SMTP services using invalid TLS certificates (e.g., self-signed certificates) when the client system is not configured to use a system-provided PKCS#11 store. This allows a meddler in the middle to present a different invalid certificate to intercept incoming and outgoing mail.
You can find information about how to handle this issue in the security team's documentation.