Another workaround to launch the game from steam is to open the properties window of ksp2 and setting the launch options to the complete path to your KSP2_x64.exe in double quotation marks ( these: " ) and after that %command%.
for most the most people the path would be C:\Program Files (x86)\Steam\steamapps\common\Kerbal Space Program 2\KSP2_x64.exe
so your launch options should look something like this:
"C:\Program Files (x86)\Steam\steamapps\common\Kerbal Space Program 2\KSP2_x64.exe" %command%
