My iMac is compatible with Big Sur, but I cannot get it to even update to High Sierra or Catalina. No updates are available through the App store even though I am running an old OS.
How can I get my OS to update when it says no updates are available. I'm running Sierra version 10.12.6 on an iMac (Retina 4K, 21.5 inch, Late 2015). Even getting to Catalina would be great, Big Sur even better.
iMac 21.5″, macOS 10.12
