Explanation
Box 1: Tier 1
For evaluation and analysis use Tier 1 sandbox.
Box 2: Tier 1
For Golden Configuration use tier 1 or tier 2.
Box 3: Tier 2
Tier-2 environment: Standard Acceptance Testing - One Standard Acceptance Testing (UAT) instance is provided for the duration of the subscription. This instance is a non-production multi-box instance that customers can use for UAT, integration testing, and training. Additional sandbox/staging instances can be purchased separately as an optional add-on.
Note: User acceptance testing (UAT) can use Tiers 2-5 sandbox.
Reference:
https://learn.microsoft.com/en-us/dynamics365/fin-ops-core/fin-ops/imp-lifecycle/environment-planning
https://learn.microsoft.com/en-us/dynamics365/fin-ops-core/dev-itpro/deployment/cloud-deployment-overview