Sony What's your understanding of the Medium and Small Lossless Compressed RAW in some Sony cameras?

I started looking for detailed information on this while testing to see if Darktable ever added the Lossless Compressed RAW. I figure many of you already know this, but it doesn't seem to be written down in clear terms anywhere.

Sony added the M and S options for Lossless Compressed RAW to the A1 and A7 IV via firmware. I believe the A7R V was released with these options, and while I don't know for sure, I am guessing anything from then on, so probably the A9III and the A7cII and cR.

I became curious over what the different sizes mean, exactly. Even reviews of other manufacturers that offered this feature much earlier weren't clear. Early reviews simply state the camera 'uses fewer pixels', which sounds to me like choosing APS-C mode. To further complicate this, the M file size is exactly the same number of pixels as APS-C. So, why do I need two ways to create a smaller file of the exact same size?

After more digging, I found the answer in a review of the A7R V. Sony clarifies that in the M and S modes, the camera uses the entire sensor to record the image then down-samples the information to fewer pixels. This preserves all of the detail of the higher MP sensor. For example, a 21MP Medium Lossless Compressed RAW file from the A1 would supposedly have more detail than a standard file from a 21MP FF sensor. I couldn't find much about DR, I would assume it doesn't preserve the same as a large file, but would think that since it's using the entire sensor, some advantage from the FF in low light is preserved.

I confirmed this to some degree by some simple field testing. If I set the camera up for Lossless Compressed, the image remains the same in the viewfinder regardless of which size is chosen. Conversely, if I choose APS-C mode the image is magnified, as expected with a crop sensor image.

As stated at the outset, my initial goal was to see if Darktable (finally) recognizes Lossless Compressed RAW files from my cameras. I learned that while they do see the L file, they cannot open the M and S files, but they are viewable as thumbnails. Frustratingly, FastStone Image Viewer can read and open the L files, and it can open the M and S files, but the latter are not viewable as thumbnails. DXO sees the L, but not the M and S at all, which is the same thing MS Photos with a RAW viewer plug in does.

At some point I'll do some more testing to see if Affinity Photo will read them, but honestly don't see the point in my use-case for smaller files, same as I don't see the need for APS-C, although others put them to good service, just not for me. The only reason I would want a smaller file is for storage, and simply changing from Uncompressed RAW to Lossless Compressed Large saves almost 40% on the card and computer.

If anyone has a different understanding of this or if I'm missing something, please post.