If you are using GOG Galaxy, then please open the Galaxy Client, click the game, click MORE > Settings, here add the following launch parameter:
and check if this makes a difference.
If you are not using Galaxy, please go to the game installation folder (by default: C:\GOG Games\Kerbal Space Program). Once in there right-click on Launch Kerbal Space Program, and select properties. In Properties window, switch to Shortcut tab, and here add this parameter at the end of Target field:
If the game is installed to default installation folder, then the Target field should look like this:
"C:\GOG Games\Kerbal Space Program\KSP_x64.exe" -force-opengl
After that press Ok, to apply settings and start the game using the modified shortcut. If you are using a desktop shortcut for this game, please replace it with this one.