Keynote v11.2 is exclusively for Big Sur or later operating systems. Keynote v11.1 is the last version available for Catalina.
Launch the Mac App Store and be signed in to it with the same Apple ID used to previously install Keynote. Press cmd+0 (zero) to open the Purchased panel. On there, you should see Keynote with an Update button. Click that. A dialog will appear advising that you need a newer version of macOS to get Keynote. Do not click Cancel, and just acknowledge that dialog. A second dialog may then appear offering to install the last compatible version of Keynote for Catalina. Acknowledge that dialog and you should discover Keynote v11.1 installed.
For what its worth, iBooks Author still works on Monterey 12.3, but that could change as Apple is no longer supporting it, and future changes to the operating system could render it inoperable.