Cataclysm is a new engine, so yes, you must compile it to see liquid. If you can get the generic 4.12.5 engine compiling with Development Editor for Win64, then you should be able to use that as a starting point and pull the Cataclysm code into that branch. Then do a clean build.
I would suggest making a local repository getting the 4.12.5 branch and running the setup.bat file to get all the files you need to build the engine. Then you can use that as the base for the CataclysmDemo branch and pull the new engine in. running setup.bat after getting the CataclysmDemo branch may overwrite some nvapi binaries that are newer in Cataclysm then they are in generic unreal. Anyway, the important thing is, if you can get generic 4.12.5 compiling then I hope you will have no problem getting CataclysmDemo up and running.
You mentioned commits and syncs. You should not have to do any commits, just pulls to get the code. As a side note, any commits you do to your local repository won’t show up in the remote branch unless you push them to it.
Good luck,
Maybe this will help: Setting Up Your Development Environment for C++ in Unreal Engine | Unreal Engine 5.3 Documentation