Image gallery glitch on mac?

Trying to put an image in a definition, I assume Image Gallery is the way to do it but I can’t find a way to do it with this dialogue box. Is this a mac problem or an I missing something.

I see this. That’s not right. This is a case of incomplete implementation on macOS. Logged in RH-45927. Thanks for reporting this.

The image gallery component is much improved in the latest RhinoWIP. Please give it a try.