What test level will be enforced when deploying a user story with Apex components from UAT to production set to NoTestRun?

When deploying a user story with Apex components from User Acceptance Testing (UAT) to production with the setting for NoTestRun, the test level enforced is "Run Local Tests."

This designation implies that only tests associated with the changes being deployed will be executed, specifically those that are either written or influenced by the relevant Apex classes and triggers in the source environment. This approach reduces deployment times because it avoids running all tests that might not be relevant to the current deployment, therefore streamlining the process, while still ensuring that the attached tests to the components are adequately assessed during the deployment process.

Choosing to run all tests or specified tests would be excessive in this instance since the "NoTestRun" option signifies that the deployment is likely being done in a controlled manner where the expectation is that only local tests need to be validated prior to deployment, accounting for the stability of the changes already verified in the UAT environment.