Open Gallery In New Tab

Is there a way to (click on a photo from album) force a gallery (in the middle of a blog-page) to open in a new tab?

No – all of Photonic’s galleries open in the same page, in a lightbox. This is intentional, as Photonic is a gallery and lightbox plugin.

I have tried this in Generic Settings:
External Link Handling -> Let the links to external sites (like Flickr or Instagram) open in a new tab/window.

But this is not working

The intent of this setting is to open the Flickr page or the Instagram page (not the Photonic page) in a new tab. E.g. if your photos had a caption, the caption would show up in the lightbox with a link, and when you clicked on that link you would be taken to external pages. I don’t think that works for Google Photos though, due to user permissions.