Hi, I have the same problem - annoying shadow flickering.
I tried:
- change my resolution 2560/1440
- change vertical sync
- change fps limit
- install and uninstall graphic mods. To clarify, the shadow problem appears in a clean KSP without mods
- change fullscreen / window
- use the -force-d3d11 launch option
- reinstall the game
- use geforce experience optimal settings. I have - rtx 2060 super - just turn off the shadows and it kind of works, fixes big black lines, but leaves shadows flickering. It's on the my video My "shadow flickering" issue video