List of compatibility: Mac OS from 10.15 to 10.9
Here is a list by operating system, that lists what Mac Model that has that operating system as the newest version of mac OS available to it.
10.15 macOS Catalina
MacBook introduced in 2015 or later
MacBook Air introduced in 2012 or later
MacBook Pro introduced in 2012 or later
Mac mini introduced in 2012 or later
iMac introduced in 2012 or later
iMac Pro (all models)
Mac Pro introduced in 2013 or later
10.14 macOS Mojave
All who support Mojave support macOS Catalina
Except:
Mac Pro introduced mid-2010 or mid-2012 models with a recommended Metal-capable graphics card.
10.13 macOS High Sierra
MacBook introduced in late 2009 - mid 2010
MacBook Air introduced in late 2010 - mid 2011
MacBook Pro introduced in mid 2010 - late 2011
Mac mini introduced in mid 2010 - mid 2011
iMac introduced in late 2009 - mid 2011
Mac Pro introduced in mid 2010 - mid 2012(will support Mojave if it has compatible graphics card)
10.12 macOS Sierra
All macs who support macOS Sierra support High Sierra.
10.11 OS X El Capitan
MacBook (13-inch, Aluminium, Late 2008)
MacBook Air introduced in late 2008 - mid 2009
MacBook Pro introduced in mid 2007 - mid 2009
Mac mini introduced in early 2009 - late 2009
iMac introduced in mid 2007 - early 2009
Mac Pro introduced in early 2008
10.9 OS X Yosemite
All who support Yosemite also support El Capitan