Hello ,
Same problem here , since yesterday i've tried everything uninstall / move / disable firewall and other / and verify nothing change.
put the missing folder from kerbal 1 to kerbal 2 nothing ... uninstall ksp1 and all component and install ksp2 nothing again.
the only solution for me : i can launch the game from KSP_x64.exe (without steam)
i hope this problem will be fix soon ^^