Hi!
To get the lightbox to open in the classic editor, you’d insert an image using the Add Media button. Once it is inserted, click on the image and click the edit/pencil icon which will open the image settings. And then set the image to open media file. That should do it. Give that a try and let me know if it’s working for you.
Out side the classic editor, I have update the plugin so it will open images without needing to set it as Link To: Media File. I will plan to extend that to Classic Editor so this extra step is not necessary.
