You can modify the way Copper renders your PCB layout. There are various options that are very useful. Tap on this icon in the Layout section of the bottom tab bar.
If activated, displays all layers. If disabled, all layers that compile the opposite side of the board are hidden. This way you ca quickly hide all bottom layers for example (bottom, bStop, bCream, bRestrict, bNames and bValues). You won't need to disable those layers separately in the layer list.
Copper correctly calculates copper fills for polygons. Sometimes, those large fill areas hide details from the opposite layer. Use this option to disable rendering copper pours. It will not disable rendering of all polygons, just the pours of top and bottom layers.
If you want to see the board from below, you typically need to wrap that in your head. With Copper, you can just flip the orientation, layer hierarchy and many more with this option. If you switch the layer to bottom, Copper will render the board exactly as if you would flip the board in real life.