How to crop 4:5 using the Photos app
If you choose the crop tool in the Photos app, and then tap the crop presets button at the top right (looks like solid rectangle in another rectangle), you get some presets: Original, Freeform, Square, 9:16, 8:10, 5:7, etc.

But you want 4:5?

Just use 8:10. 4:5 = 8:10, right?