hello! I have mac mini Macmini7,1 with Sierra 10.12.6. I need to install new MacOS, but I don't have any updates in Software Update or App Store. Why and what should I do to get macOS Big Sur for example and install on my mac mini?

The 7,1 Mac mini is a Late 2014 model.

see > Identify your Mac mini model - Apple Support

It can be update and run all the way up to macOS 12 Monterey.

see > How to download macOS - Apple Support

However coming from OS X 10.12 Sierra, you should go to 10.13 High Sierra first.

Then choose one of the earlier macOS's like Mojave or Catalina, before moving to Big Sur or Monterey.

Back up your data, check the application compatibility table, click on the second link den.thed posted above, and then on the one for a more-recent OS. They're full-version upgrades and won't appear in the Updates list.

Catalina and above won't run 32-bit software; if you choose one of them, use Go64 as well.

(239622)

+1 Thank you Niel.

To Elena

You will not find them at the App Store.

Open the How to download macOS - Apple Support link and click on the macOS version that you want.

You're welcome.