Smooth Transitions between the levels

1 - Add a cube in your players head with a translucent material, black, fill its opacity

2 - Add a splash screen

3- Call load level

4 - When the other level loads, clear the splash screen
5 - Fade out 

Thank you for the reply.
Will the below solution work?

You are missing one thing tho:
Start Camera Fade doesn't work AFAIK.
you gotta animate the transition cube material manually, other than that, yes!

Yes. I tested also. Start camera fade don't work. For transition cube material, do I need to use dynamic material? 
Will that work on quest? 
Do you have any tutorial video?

Not at the moment, but you can search for animate a material parameter in a timeline.

It works on quest yes, that's how I'm approaching it in my projects

you can animate a node called "set color scale and offset", fade in and out of levels.
I attached 1 image demonstrating. the timeline is animation a vector from black to white. I break the vector to get the RGB values. alpha is always at 1
to do the opposite effect, go from white to black