Collage creator?

The previous collage feature isn't currently available within the new Adobe Express. However, it is a feature that's been requested and is planned. You can check on the status and add your vote to this feature here: 

https://adobeexpress.uservoice.com/forums/951181-adobe-express/suggestions/46769416-photo-collage-as-per-the-previous-express

You will notice that in that topic there are now Grids in Adobe Express, and they are quite versatile. You can see Andy demo them in this video:

https://www.loom.com/share/c7eb2a7bf6394b04b4cda2c5b3279ceb?sid=1e1576df-dbd8-4ef0-b195-ffba15facb22