Macbook Retina 12" 2015. Can I still update the software?

Hi,

Unfortunately, the MacBook Retina 2015 will not update beyond MacOS Big Sur 11.7.9. You also will not get any security updates, as 11.7.9 was the final one for that model. Sorry for the inconvenience.

macOS Big Sur is compatible with these computers - Apple Support

A definitive answer requires identifying your specific model MacBook: Identify your MacBook model - Apple Support.

To learn how to update macOS, please read Update macOS on Mac - Apple Support. An "early 2015" model can be updated to run macOS 11.7.9 "Big Sur".