When users begin working with Power Apps, the usual thing to do is to register for the Microsoft 365 program and to then create a Power Apps Developer Environment.

https://learn.microsoft.com/en-us/office/developer-program/microsoft-365-developer-program-faq

This offers a licenced way to access SharePoint and build Dataverse apps for training and development purposes.

Many online resources (which includes the official Microsoft Learn pages at the time of writing) prompt the user to create a developer environment by following the instructions on this page:

The problem is that when we click the "Existing user? Add a dev environment", an error message appears that says "You need a Power Apps license to use this app".  This error is clearly wrong because it shouldn't be necessary to have a license to add a "dev environment".

As an aside, If you're not sure what the reference to the "Community Plan" in the error message means, the "Community Plan" was the plan that pre-dated the "Developer Plan" in 2021. The "Community Plan" was more limited than the "Developer Plan" because any apps that were built in the "Community Plan" could not be shared with others.

This error appears to originate from an enhancement that Microsoft made to enable all users to have up to 5 developer environments, which ultimately is an improvement.

if you want to add a developer environment, a working way to do this today is to log into the preview portal using the link below (note the presence of preview in the URL - this is important):

https://make.preview.powerapps.com/

From here, you can click the environment name in the top banner to open the panel that’s shown in the screenshot beneath.
 

In the "Need your own environment? (It's free)" panel, you can click the "Try it now" button. This displays the following view to create a developer environment. After choosing an environment name and region, you can click the "Accept" button to create your new developer environment.