Hi Michael,
I think you are mixing up PowerClient and PowerServer. PowerClient is already released as new feature of PB 2019 R3 while PowerServer 2021 will be newly supported in PowerBuilder 2021.
PowerClient automates the install and updates of client/server apps. Your apps remain as client/server with local database connection. The following feature tour will educate you of what PowerClient is: https://www.appeon.com/products/power-client
PowerServer converts your client/server app into a cloud-native app. So as Francisco mentioned, your app does not directly talk to the database but rather consumes its data through REST APIs and the REST APIs is what talks to your database. The following architecture diagram illustrates how this is different than client/server: https://docs.appeon.com/pb2021/whats_new/PowerServer_deployment.html#Architecture
So long story short, if you want to stay client/server and just get rid of headaches of keeping apps updated to your users then go with PowerClient. If you are currently using VDI (e.g. Citrix, terminal services, etc.) or need to deploy your app over the Internet go with PowerServer.
Best regards,
Armeen