As with any hibernation state, there is a moment where the subject wakes up. So will be the case of the apps that are put by the system (automatically) or by the user (manually) in that state. Once the user decides to wake them up, the apps are uncompressed.
However, until Android 12 arrives, the manner in which apps will go into hibernation is still up in the air. We’ll have to wait and see how Android will implement this very useful, very timely feature.