JoomlaWorks website: Simple Image Gallery
https://www.joomlaworks.net/extensions/free/simple-image-gallery
Description extracted/translated from the site
Simple Image Gallery by JoomlaWorks, is an image display plugin (gallery).
The free version does not do everything, but it has the advantage of being extremely easy to use.
This plugin can transform any folder of images contained in your Joomla site into a gallery of the "grid" type with "previews"
nice lightbox type (using opensource fancybox), simply by using the following syntax (tag gallery)
{gallery}myphotos{/gallery}.
Example:
For example, if we have a folder named my_trip_to_Paris located in the images/stories/my_trip_to_Paris folder, and the plugin's base folder has been declared as images/stories, we can create our gallery by simply entering the tag {gallery}my_trip_to_Paris{/gallery} in an article Joomla.
The created galleries are presented in a grid with a background of the "polaroid" type for miniatures.
When visitors click on a thumbnail, they have access to the original image in a "lighbox" popup.
Miniatures are generated and cached with PHP for best results.
I maintain a fork on github https://github.com/JLTRY/simple-image-gallery/tree/master
and I updated the plugin for Joomla 5.x