Agnostic

I have downloaded 5 3rd party VST apps unzipped into a "VST" directory in the "App Data"\...\NCH folder. One of them was visible to the program, but it did not sport a .DLL file, rather a group of 4 .SEM files. The others sporting .DLLs are still invisible. My question is in version 12.52, What file types are supposed to work and where must they be installed in order to be seen? My conclusion at this point is that .DLLs are not going to work which is a great disappointment.