As a test, in Windows Rhino, I create a cube and plunk a texture on it via dragging and dropping an image file from a folder in my Dropbox onto a Rhino object. (why can’t you DnD textures like that on Mac??) I have “Save support files in 3dm file” checked, I save the file. If I re-open it later on a Windows Rhino, even if I have moved/deleted the original texture image, the texture still shows up, as it has been saved in the file.
However, opening the file on Mac, the cube comes in as gray, no texture to be seen. I select the object, and in Properties>Material, neither Layer, nor Parent nor Object is checked. I click Object, but the panel below is blank. I click Layer and then back to Object and the panel shows up. “Texture” is already checked, with the path to the texture file, indicating that the object has had a texture applied. Obviously it’s the path from Windows, so it’s wrong for the Mac. But the texture has been saved in the file! It’s in there! RhinoMac can’t find it.
OK, let’s go the other way – create a copy of the file on the Mac, go in and re-reference the textures from the Mac side so they show up, then save and quit. Open the copied file in Windows or Mac and bingo! - the texture is there. Delete the original image, it’s still there. So the Mac is capable of saving the texture in the file – in fact, I don’t see any way to NOT have it do that – so why isn’t it capable of reading the texture already in the file that has been saved under Windows?