The latest OS this model supports is Mac OS X 10.6.8. As far as I know, there are no logic board upgrades which can change this. You may be able to find a firmware patch/hack that allows you to install Catalina, but I wouldn’t recommend doing this because Catalina is not designed to run on any logic board designed for your system and a patched installation would likely lead to poor performance or glitchy behavior. Unfortunately Dan is right - if you need to run the later OS’s trying to upgrade this machine just doesn’t make sense, from both a cost and effectiveness perspective.