Build engine does nothing, no error, changes not reflected

My UE5 C++ solution in VS2022 has two projects, UE5 and the game itself. The game compiles just fine. However if I make any mods to the engine source, then click build, it instantaneously says build succeeded, does nothing, and any changes are not reflected. Is this happening because the ‘source’ that is in there is just for reference and cannot compile to an executable engine without downloading the source from github? This is a port from a UE4 project which did indeed have the UE4 source… so I am not sure what happened during conversion but the engine source for UE5 appears to be there, and the only problem is compiling says all good but does nothing.