Which annotation stops an immediate child resource's health from counting toward its Argo CD application's health?

Answer: argocd.argoproj.io/ignore-healthcheck: "true"

Explanation

Setting argocd.argoproj.io/ignore-healthcheck to "true" on an immediate child resource removes its health from the application's aggregated health. The resource still has its own health status, it just no longer counts. Use it sparingly, since an ignored Deployment that crashes will no longer turn the application Degraded.