I have an iMac late 2012 model with OS Mojave 10.14 installed

You can upgrade to Catalina (macOS 10.15.7) which is the last upgrade for your Late-2012 iMac. Because you are currently on a version of macOS that still supports 32/64-bit applications, it might be useful to check what 32-bit applications you have now, that are unsupported on Catalina. I suggest you download and run the free Go64 application to determine those applications.

You should verify with your third-party application, printer, and scanner vendors if they support Catalina before you upgrade. Some may have specific updates to that end. Others may not.

You should also consider it mandatory to perform a Time Machine backup of Mojave before you upgrade to Catalina.

Using only the Safari browser, visit How to get old versions of macOS for the link to Catalina in the Mac App Store.

The latest your 2012 iMac can run in Catalina 10.15.7, you can find it at How to get old versions of macOS

Consider if it is worth going to Catalina. Does Catalina have any features you want or need vs Mojave?