Give it 5-10 minutes. If it does not go further, and your PC is not sending you signals that it is still working, like sounds and HDD LEDs flickering, then try to terminate the game.

Once back in Steam, right click KSP2 and choose “properties” from the menu. In that screen choose “local files”, and then click the button that says “verify integrity of game files”.

Once that is done, launch the game and see if it got fixed.

This will make sure all the files of the game, that were downloaded while installing, are not damaged and identical to the originals from the developer. Downloading sometimes causes hickups that can slightly damage/corrupt a file.