Unable to access Leica c-lux RAW picture files with 15 inch MacBook pro with OS 10.14.5

What is the exact model name of your camera? Is it on the list of supported cameras?

Here is a list of the RAW formats you can use with Photos for Mac: Digital camera RAW formats supported by iOS 12 and macOS Mojave - Apple Support

I am seeing several Leica D-Lux models, but not a C-Lux model.

if your camera is not on the list, you may have to wait, if Apple will support the RAW format of this model as a part of a next system update. For the time being, you could use the software that came with your camera to convert the RAW files to another lossless format like TIFF, or try the Adobe DNG Converter to develop the RAW files to use with Photos. https://supportdownloads.adobe.com/product.jsp?product=106&platform=Macintosh

I don't have a Leica camera, but usually a camera manufacturer includes a download link in the user guide for software to process the RAW files, if a camera can shoot RAW. The RAW format is always camera specific and you need a RAW converter for this model.

Adobe's DNGConverter is free (https://supportdownloads.adobe.com/detail.jsp?ftpID=6673). I could always use it without a subscription for Lightroom or Photoshop. Adobe supports these Leica Cameras: https://helpx.adobe.com/camera-raw/kb/camera-raw-plug-supported-cameras.html#Leica

I remember, that the RAW Support page for Aperture mentioned restrictions for DNG files, see the footnotes 1 and 4: https://support.apple.com/kb/SP772?locale=en_US

1. DNG files must be generated by the Adobe DNG Converter with the “Convert to Linear Image” option turned off.

...

2.Aperture works with most DNG files generated from cameras that support this format and with DNG files generated by the Adobe DNG Converter with the “Convert to Linear Image” option turned off.

The new RAW support document for the current system (Digital camera RAW formats supported by iOS 12 and macOS Mojave - Apple Support) does no longer list all the small print from the Aperture version, but I suspect they still apply.

Strangely enough, I believe that Leica's create DNG's, but it is odd flavor of DNG's that the Mac DNG converter can't read. So a DNG conversion in this case will be pretty benign.

DNG is a really weird standard, isn't it, Keith? It would be too easy if there were just one DNG format, to make them compatible on all devices.

I think the problem is that most decoders just decode what Adobe converts to, and do not worry about all the other options, like linear vs log data in this case.