I assume you are familiar with Power Automate and know how to create an automated cloud flow for a specific environment. But just in case, let's quickly review these steps.

The first step will look like this:

Step-by-Step Guide to Get Current Power Automate Environment

On the second step, we are saving email data to a variable:

Step-by-Step Guide to Get Current Power Automate Environment

Now, the important part.
Add a "Get Environment as Admin" action from the "Power Platform for Admins" connector.

Step-by-Step Guide to Get Current Power Automate Environment

After that, you need to add a "workflow()['tags']['environmentName']" function as a custom value in the environment on the Parameters tab.

How To Navigate Power Automate Environments - Step-by-Step Guide

As a result, you will receive a lot of information about the environment where this flow is running, but we are especially interested in the Name field because this is where the ID of the environment is stored.

You can find the environment ID value on the Power Platform admin center environment page:

How To Navigate Power Automate Environments - Step-by-Step Guide

In the next step, we will create a condition to check if the current environment is a Sandbox environment:

How To Navigate Power Automate Environments - Step-by-Step Guide

And if it is a Sandbox, we will replace the "email" variable value with our demo testing@t1e2s3t.com email in the True branch of this condition:

How To Navigate Power Automate Environments - Step-by-Step Guide

And that's it!

If a newly created Contact has an email and a record creation happened in the Sandbox environment, the email value will be replaced with testing@t1e2s3t.com.

Of course, many organizations have more than two environments, and in this case, you just need to create another similar condition in the False branch of the first condition.