Updating a Macbook Pro - what is the latest version that is supported?

Note that you list a 14" MacBook Pro in your post with macOS 14.2. That will support the current and lates version released -- macOS 14.3

If you are asking about some other MacBook Pro, what is the model year of the MacBook Pro? 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.

A mid 2010 through late 2011 MacBook Pro can be upgraded to High Sierra 10.13.6 but no later version. 

A mid 2012 through early 2013 MacBook Pro can be upgraded to Catalina 10.15.7 but no later. 

A late 2013 and mid 2014 MacBook Pro can be upgraded to the latest version of Big Sur macOS 11 but no later. 

An early 2015 through 2016 MacBook Pro can be upgraded to the latest version of Monterey macOS 12 but no later. 

A 2017 MacBook Pro can be upgraded to the current version of Ventura macOS 13. 

For all of the above, see instructions in: How to download and install macOS - Apple Support  

A 2018 or later MacBook Pro can be upgraded to the current version of Sonoma macOS 14. See: How to upgrade to macOS Sonoma - Apple Support

MacOS Sonoma 14.3 is the current MacOS.

As far as what the last supported version that's supported on YOUR Mac, you didn't tell us which Mac you have (including the model year). So we have no way of knowing.