

Only if you have stored files locally and select “also delete local data” when deleting the app. You can check this in the Files app or by connecting the device to a computer and browsing the books storage section.
Anything backed by icloud storage (and of course anything purchased from the store) can be redownloaded later.
As a compromise, you can “offload” the app until you’re ready to use it again from the apps section of settings. This has the side effect of retaining existing data while uninstalling the app itself.
A version of this that’s fooled me involves the multiple desktop feature in some graphical OSs (I think Windows calls them workspaces).
The entire point is to clear out your dock/taskbar this way but occasionally I’ll forget, heave a dramatic sigh, and begin troubleshooting before it hits me and I sheepishly return to my work.