Configure your secrets in Azure Key Vault (AWS Secrets Manager, GCP-something-I-forget) or whatever the non-cloud Vault software is called.
Devs only set client_id, client_secret, and env defaulted to dev. On startup, the app fetches configs for the secret store. The needed secrets are in source control. If the needed secret is missing from the secret store, there is a clear error on startup.
You are welcome, I just saved you weeks of onboarding, confusion, and devs passing around .envs on Slack.