Unfortunately, nobody replied. I found this and it helped me: New tutorial: CMS Galleries made easy
Only one issue that is left with this hack and also another hack is the following: On my iPad the big image is not full size. It’s like 40% width of what it could be and therefore not much bigger than the thumbnail.
I have this issue on SOME iOS/iPad devices with Google Chrome AND Safari. I Recorded a video here: - YouTube
Page showing in the video: http://idext.webflow.io/gallery-dont-delete
Read only link: https://preview.webflow.com/preview/idext?preview=52b09780276c8273d0b6b78678ec33bb