I finally found the download button in the Lightgallery lightbox. When logged in as an admin, it was buried under my admin menu
Not sure I am following you. The default configuration for LightGallery is to show the download button, not hide it. So if you enabled LightGallery as your lightbox you should be seeing the button enabled by default without having to do anything else. In fact, the setting in the admin menu is to disable the button, not enable it.
However, clicking on the download icon just opens a new browser tab and doesn’t actually download the image.
Can you share a link here so that I may troubleshoot?
On another note. I am trying to load multiple galleries in tabs, using the DIVI theme. The first tab looks correct, with images being displayed in 3 columns. All the other tabs will only load the images in a single column. If I change around the order of the tabs, the first tab is fine. The others single column. Any ideas around that?
You will have to work with the provider of your tab component for that. Without a URL what I can suspect is that whenever a tab is selected you will need to trigger a jQuery window resize. The better tab plugins let you attach such custom JS calls to them, so you might want to start with your theme’s support for this.