The package description doesn't do a particularly great job at explaining what this is:
This is the German "Coroana Warn App"[1], the official German contact tracing app but instead of using Google's Exposure Notification Framework (ENF) it relies on the microG implementation of the same API. It can either use a system-level microG implementation or fall back to the bundled implementation running purely as an app without any system permissions.
This makes the app fully free and 100% compatible with the upstream google based version.