What is Subscriber Arcade on the new apple games app?

Discussions of iOS 26 features is a violation of the terms. This is a Support Site and currently support is not available for the beta software.

Yes, the beta software is Apple confidential information. Don’t install the beta software on any systems you don’t directly control or that you share with others. Don’t blog, post screenshots, tweet, or publicly post information about the beta software, and don’t discuss the beta software with or demonstrate it to others who are not in the Apple Beta Software Program.

Apple Beta — FAQ

You are free to view the information Apple has made available on their own, but you will not find any Support.

OS - iOS 26 - Apple

The public iOS 26 Preview page says that there will be a new Games app to help manage games.

Not that games will be free.