If you can't see your media files after updating to Mylio Photos v24, it is likely that you are in an incorrect Space. Spaces is a new feature in Mylio Photos v24. You can learn all about spaces in this mini-course.
To resolve the issue you're seeing, click on Spaces in the Left Sidebar and select Everything. You can see what space you're working in by looking at the space name at the top of the window:
On mobile, the Spaces tool can be found under the More Menu (the three dots in the top-right):