Hi there!
It seems that you save your file as a Luminar project file (its file extension is .lmnr). Your work is saved in its current state so that you can later continue from the same point. In this case, this .lmnr file stores history states, layers, filters, masks, etc. That is why Luminar project file can be rather big. You can also save image files from your Luminar project. These files are broadly compatible with many other applications. All you need is to Export the file. When you export a file, you can save in a variety of file formats including JPG, TIFF, PNG and even PSD.