Can't Update My Keynote

If you had previously installed Keynote from the Mac App Store on earlier releases of macOS, you may be able to get the last compatible version of it for Catalina.

Launch the Mac App Store, and sign in with the same Apple ID you had used to install Keynote previously. Press cmd+0 (zero) to open the Purchased screen, and if Keynote is there with a blue cloud outline next to it, click that. It will open a dialog offering to install the last compatible version (v11.1) of Keynote for Catalina. That would also work to get Pages v11.1, and Numbers v11.1 too.

Hi balots,

Thanks for coming to Apple Support Communities for help today.

You will need to see if you're able to update your Mac to Big Sur. Please see: How to get old versions of macOS and macOS Big Sur is compatible with these computers.

Have a fantastic day!

You are welcome.