Setting environment in .env - can't get it working

I downloaded a fresh copy of CI4 from the development branch. The default welcome page displays environment -

Code:

Page rendered in {elapsed_time} seconds. Environment: <?= ENVIRONMENT ?>

I, then, created a copy of "env" to ".env" and only added this line

CI_ENVIRONMENT = production

I still see environment as "development"

I can't find any settings which i can change in config/app.php

What am I doing wrong?