2012 Macbook Pro Won't Update

What is your current macOS?

You may have to stair step up

Verify you meet all the - Technical Specifications—OS X 10.11 El Capitan :

https://support.apple.com/kb/SP728

How to upgrade to OS X El Capitan - Apple Support

https://support.apple.com/en-us/HT206886

MacBook (Early 2015)

MacBook (Late 2008 Aluminum, or Early 2009 or newer)

MacBook Pro (Mid/Late 2007 or newer)

MacBook Air (Late 2008 or newer)

Mac mini (Early 2009 or newer)

iMac (Mid 2007 or newer)

Mac Pro (Early 2008 or newer)

Xserve (Early 2009)

Go from there

Typically you are always better off running the most current macOS you machine will allow—especially for the built in security features.

macOS 10.14 Mojave - Technical Specifications:

https://support.apple.com/kb/SP777

Upgrade to macOS Mojave - Official Apple Support

https://support.apple.com/macos/mojave

https://itunes.apple.com/us/app/macos-mojave/id1398502828?mt=12

MacBook (Early 2015 or newer)

MacBook Air (Mid 2012 or newer)

MacBook Pro (Mid 2012 or newer)

Mac mini (Late 2012 or newer)

iMac (Late 2012 or newer)

iMac Pro (2017)

Mac Pro (Late 2013; Mid 2010 and Mid 2012 models with recommended Metal-capable graphics cards)

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macOS 10.13 High Sierra - Technical Specifications:

https://support.apple.com/kb/SP765?locale=en_US

How to upgrade to macOS High Sierra

https://support.apple.com/en-us/HT208969

MacBook (Late 2009 or newer)

MacBook Pro (Mid 2010 or newer)

MacBook Air (Late 2010 or newer)

Mac mini (Mid 2010 or newer)

iMac (Late 2009 or newer)

Mac Pro (Mid 2010 or newer)

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If you can run macOS 10.12 Sierra, you can run macOS 10.13 High Sierra

https://itunes.apple.com/us/app/macos-sierra/id1127487414?ls=1&mt=12

The 2012 MBP is quite capable to run Mojave and Catalina when it released in the Fall.