I have an iMac (27" late 2012) with OSX Yosemite 10.10.5. Is there any system update available for this iMac?

A Late 2012 iMac can run up to macOS 10.15 Catalina.

To update see > Update macOS on Mac - Apple Support

Back up your data, check your applications for compatibility, click here, and then on the download link for a newer OS. Its maximum is Catalina.

Catalina and newer won't run 32-bit software; download and use Go64 as well as using the first link above.

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