No, Cloud Functions need Blaze since 2020, regardless of version. But Blaze includes the same free quota (2 million invocations/month), so one welcome email function will cost €0 in practice.
To remove the fear:
- Set a budget alert in Google Cloud Billing (e.g. €5). Note it alerts, it doesn't stop spending.
- Set
maxInstances: 1on the function so a bug can't fan out. - Container images for functions are stored in Artifact Registry, and old ones can cost a few cents. Set a cleanup policy (
firebase functions:artifacts:setpolicy).