Update: There is no longer a three-export limit in the Starter plan for the desktop version of Premiere Rush – Adobe removed this limit in version 2.0 last week.
Basically, Rush on desktop now acts the same as Rush on mobile – the no-cost plan gives you unlimited video exports with a "freemium" model that offers use of most of the features and content.
If you want to use Rush's premium features and content in your exported videos, then that's not included for free and a paid plan is required.
In addition, there were also some important changes made regarding Premiere Rush and the Photography plan. Here is Adobe's messaging about that:
"That's right! We've added premium access to Premiere Rush and Photoshop Express to all plans that included Spark premium. There won't be any changes to the cost of your subscription. Let us now if you need any help getting started with PsX or Rush!"
These additions apply only to current/existing customers in order to replace Spark premium, which was removed from the Photography and single-app plans at the same time.
More details on all of this covered here:
Premiere Rush Free Download: What's Included in the Starter Plan?