Hi there,
Thanks for reaching out. I'd like to inform you that in the Creative Cloud Express mobile app (iOS & Android), all the projects (self-made or shared) come under the "Your Projects" tab. You may find every project you worked on or shared with you in this tab.
Also, You may log in via express.adobe.com from a web browser on a computer and then click on the bell icon at the top right corner to approve the invitation. Once the share request is approved, the projects will be available under the "Shared with You" tab in the "Projects" option from the sidebar on the web browser and under the "Your Projects" section on mobile devices.
Let us know how it goes.
Regards,
Amitej