@Corissandageri ,
Depending on what is in your gallery images (attachments, library items or URL) you can open them individually Attachments
Launch(ThisItem.AbslouteUri)
Library
Launch(ThisItem.'Link to item')
URL
Launch(ThisItem.FieldName)
where the FieldName is the one containing the URL.
You can also use Download(), but this has the same effect.
I also have a blog on SharePoint images that may be useful to you.
But back to your question, you can only launch one at a time as the browser will only open one new tab (it replaces the first if you try to open a second).
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