SOLVED. Just upgraded to 6.0.2 - My 5.1 schematics are no longer visible. Just a gray sheet

Can you start a new project and draw something visible there?

You have the grid on, so at least the dots should be visible, and also the drawing sheet and page limits unless you have changed the settings. I guess this is a rendering problem. What happens if you switch between Accelerated and Fallback graphics in Preferences → Schematic Editor → Display Options → Rendering Engine?