How to which user has uploaded in the front end?

The demo is using masonry layout, when you click on it, it will have a toolbar with a man icon. Clicking on that will redirect you to the user gallery.

Flexi has many layouts, you can change them to (eg. wide layout) to have toolbar at the front.

If you turnoff popup, will take you to detail layout which will automatically show author information if supported by theme.

May I know what are the supported theme?

This is the demo of detail page
https://odude.com/demo/flexi/flexi/women/

Theme used
https://odude.com/themes/embed-gallery/