My MacBook Pro won't update to the latest macOS version

What model year is it?

The model year of a MacBook Pro is available at Apple menu > About This Mac.

An Early 2008 through mid 2009 MacBook Pro can be upgraded to El Capitan 10.11.6  but no later version. See: How to download macOS - Apple Support

A mid 2010 through late 2011 MacBook Pro can be upgraded to High Sierra 10.13.6 but no later version. See: How to download macOS - Apple Support

A mid 2012 through early 2013 MacBook Pro can be upgraded to Catalina 10.15.7 but no later. See: How to download macOS - Apple Support

A late 2013 and mid 2014 can be upgraded to the latest  version of Big Sur macOS 11 but no later. See:How to download macOS - Apple Support

An early 2015 or later can be upgraded to the current version of Monterey macOS 12. See: How to upgrade to macOS Monterey - Apple Support

A mid 2012 MacBook Pro can be upgraded to Catalina 10.15.7 but no later. See: How to download macOS - Apple Support

Also be aware that if you upgrade to Catalina you will also need to update any non-Apple 32-bit apps. You can use the following to see if you have any: https://www.stclairsoft.com/Go64/

See the "If you can't download or install macOS" section of How to download macOS - Apple Support if necessary.

El Capitan is the operating system version that you have.

I asked for the model year -- The model year of a MacBook Pro is available at Apple menu > About This Mac.