I have a late iMac 2013 running El Capitan 10.11.16 but unable to upgrade to newer versions. What should I do?

Jojokilimanjaro Said:

"I have a late iMac 2013 running El Capitan 10.11.16 but unable to upgrade to newer versions. What should I do?"

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Ugrading a macOS:

Determine which macOS(s) can be Upgraded:

Incompatibility may be the issue here. If so, then that is because your Mac does not have the hardware to go past macOS 10.13 High Sierra.

I. Verify Compatibility:

A. Start Here: Learn About Compatibility and how to Identify your Specific Mac Model - Apple Support

B. How to Verify:

I. Reveal your Model:

What is the Model of your Mac? To find out...

1. Go to: Apple menu
2. Click: About this Mac
3. View: Second Line-Down

then...

II. Compare the Results:

See if the Model you found is shown here:

• macOS Monterey is Compatible with these Computers - Apple Support
• macOS Big Sur 11 Hardware Requirements - Apple Support
• macOS Catalina 10.15 - Hardware Requirements - Apple Support
• macOS Mojave 10.14 - Hardware Requirements - Apple Support
• macOS High Sierra 10.13 - Hardware Requirements - Apple Support
• macOS Sierra 10.12 - Hardware Requirements - Apple Support
• OS X El Capitan 10.11 - Hardware Requirements - Apple Support
• OS X Yosemite 10.10 - Hardware Requirements - Apple Support

III. If Compatible:

• Back Up your Mac First:  Be certain you Create a Time Machine Backup of your Mac, so that way you can have something to restore your Mac from, should anything go wrong with the reconfiguration.

Make sure to have a good backup before attempting to upgrade macOS.

You can run up to macOS 10.15 Catalina on a 2013 iMac.

https://eshop.macsales.com/guides/Mac_OS_X_Compatibility

However, macOS 10.15 no longer supports 32 bit apps. If any of your third party 32 bit apps don't have 64 bit versions that are compatible with macOS 10.15, then you should uninstall them by following the developer's instructions before you attempt to upgrade macOS to 10.15.

32-bit app compatibility with macOS High Sierra 10.13.4 and later - Apple Support

macOS 10.14 Mojave is the last version of macOS which still supports 32 bit apps, but Mojave is no longer receiving any updates from Apple. In fact, Catalina will stop receiving security updates later this year. You can still continue using these operating systems, but they will be a bit less secure without current updates.

Also, newer versions of macOS are locking down the root system volume containing the macOS system files. Every newer version of macOS takes an extra step to restrict write access & modifications to the macOS system files. I highly recommend if you are storing any data on the internal boot drive outside of the home user folders, that you move that data into the user folder now. The macOS installer will move it to the "/Users/Shared" folder anyway, but it will be a bit easier & less confusing if you move those items before the OS upgrade.

About the read-only system volume in macOS Catalina - Apple Support

You can find links to various versions of macOS within this Apple article along with optional instructions for creating a bootable macOS USB installer:

How to create a bootable installer for macOS - Apple Support

I highly recommend creating the bootable macOS USB installer so you have more options in case something goes wrong during the upgrade.

Don't be surprised that you end up finding out that your iMac's hard drive is bad when you attempt to upgrade macOS. An OS upgrade is stressful on an old hard drive and can reveal a drive failure during the upgrade process. If this happens, then most likely the drive was already failing, but you just had not noticed it yet.

You should always have frequent and regular backups of your computer and all external media (including the cloud) which includes important & unique data.