Where is Page to Page Transitions ?

Hi ​@NHMOODI, thanks for bringing this up!

Page-to-page transitions are available in Adobe Express, but they're currently supported only in Presentation document types and not in regular multi-page projects such as flyers, PDFs, or social media posts.

If you're working in a Presentation, you can add transitions by clicking the transition icon that appears between slides in the page navigation panel.

You can also customize the transition duration and direction, and use Apply to all pages to apply the same transition throughout the presentation. 

Please note that transitions are visible only when:

• Presenting in Present mode (full-screen), or

• Exporting the presentation as an MP4 video

If you're working with a different document type and would like page-to-page transitions to be supported there as well, I’d suggest you raise a feature request for the same here: https://adobeexpress.uservoice.com/forums/951181-adobe-express

Hope this helps!