Lightroom Classic 2020 - Cache folder empty

There really shouldn't be a need for an additional cache for Jpeg files. A Raw file consists only of sensor data, i.e. in its raw state it is NOT an RGB image and has first to be "converted" to RGB data that can then be displayed in image form. That conversion process happens every time we open a Raw file into the develop module, and it can take several seconds or longer before a "scene-referred" RGB preview is available in the system cache and can thus be displayed ready for editing in the Develop display window. So rather than have the user twiddling their thumbs waiting for the full-size RGB preview to appear, a much smaller RGB preview is created (during import or when previews are built) and stored in the Camera Raw cache. Thus when we select a raw file for editing in Develop, that CR cache entry can be loaded almost instantly, which allows us to start editing. In the background, the conversion of the raw file to produce the full-size RBG preview is done, and when complete it replaces the CR cache entry (a process which is practically seamless from a user prespective). That's probably a simplified version of the process, and there are added wrinkles which don't need to be detailed here.

But a Jpeg file, being already RGB data, needs no such time-consuming conversion process, the data can be read and displayed immediately, thus making a dedicated Jpeg cache not required.

Having said all that, if your initial query was based on performance problems that you might be experiencing, I suggest you detail those issues so that we can try to help.