One potential problem that Mac users might encounter while upgrading to a newer macOS version, is the 'macOS could not be installed on your computer' error. This particular issue may be caused by several different reasons including your Mac failing to meet the minimum requirements of the new versions, not having enough space for the update to be installed, or a software/launch daemon interfering with the process.
After trying the update process several times and always receiving the 'macOS could not be installed on your computer' error, the first thing to do is check for compatibility issues. The best method is to launch the App Store application, search for the macOS versions you are installing, and navigate to the 'Compatibility' section. Look for a message that states 'woks on this Mac.' Otherwise, your Mac is not among the supported systems for the new macOS update. The next step is to check if you have enough free space on your hard drive. As a general rule, you would want to have at least 20 GB or more that are free.
Use Safe Mode
Try initiating the macOS update while your Mac computer is in Safe Mode. This might indicate if the cause of the 'macOS could not be installed on your computer' error is a launch daemon interference as Safe mode disables all but the bare minimum of startup items, launch agents and applications. To enter Safe Mode, restart the computer, and then press and hold Shift on your keyboard until the Apple logo appears. Now try to run the upgrade process once more.
Another possible solution is to reset the system's NVRAM (Non-Volatile Random Access Memory). Unlike normal RAM, NVRAM is capable of storing data even after the Mac has been shut down or restarted. To reset it, restart your Mac and press Command+Option(Alt)+P+R on your keyboard immediately. Keep pressing the buttons until you hear a startup chime. Wait for the system to boot and try to update the macOS now.