What should a solutions architect recommend?

Explanations:

Creating policy documents in each account and assigning them to developers directly is not an ideal approach. It lacks the flexibility needed to manage access across accounts, especially as the team scales in the beta phase.

Creating an IAM role in the Development account and giving it access to the Production account is not recommended, as roles should generally be created in the target account (Production) to allow cross-account access securely.

Creating an IAM role in the Production account with a trust policy for the Development account allows the designated developers to assume the role and access resources securely in Production. This setup is scalable and aligns with AWS best practices for cross-account access.

Adding an IAM group in the Production account as a principal in the trust policy is not feasible because groups cannot be added to trust policies, which specify entities (like accounts or roles) that can assume a role.