The only version of Keynote that is available is the current version in the Mac App Store with its Catalina and Big Sur operating system requirement. Apple does not provide past, full installers for older operating systems. You can sign in to iCloud, and use the web version of Keynote on Mojave.
Your 2013 MacBook Pro can upgrade as far as macOS Catalina (10.15.7) which would gain you access to Keynote v11.0 in the Mac App Store. Catalina only supports 64-bit applications and that may be an issue if you have any 32-bit application dependency that remains supported in Mojave. I would get the free Go64 application and run it to see a list of the 32-bit software that you currently have installed, and then you can decide whether upgrading to Catalina is practical for you.
If yours is a Late-2013 MacBook Pro, it can upgrade to Big Sur (11.3.1) directly from the Mac App Store, though you will be required to have 35.5 GB of available storage before you begin the download. It is 12.2GB in size compressed.
Should you decide to upgrade to Catalina, you will need to perform a last Time Machine backup, and check third-party applications for 64-bit versions that are compatible with Catalina. That also means determining if your printer/scanner vendors provide compatible 64-bit Catalina driver support.
To access Catalina in the Mac App Store you visit How to get old versions of macOS using strictly the Safari browser.
