Portal 2 Authoring tools problem
The fix for me was to go to F:\SteamLibrary\steamapps\common\Portal 2\bin and modify the file GameConfig.txt
It contains something like "GameDir" "C:\SteamLibrary\steamapps\common\Portal 2\portal2"
Change C:\<Old Drive> to F:\<New Drive>. Also do same thing for "BSP" "Vis" ... and any other Data that defines a path.