Camera cavas on top o fworld unity
Put your UI on a Layer called UI (if it isn't already).
Duplicate your Main Camera and call it UI Camera.
Parent your UI Camera to the Main Camera.
Remove scripts like camera control, post effects and audio listeners from the UI Camera.
In the Main Camera Culling Mask turn off UI
In the UI Camera turn everything off but UI.
In the UI Camera change Clear Flags to Depth only
In the UI Camera change the Depth to something higher than the value on your Main Camera.
Then in your Canvas set the Event Camera to the UI Camera.