Hey, I can see a screenshot of your keybinding setup.
The command not found error usually means the command ID in keybindings.json is wrong. Can you check a couple things?
Open the Command Palette Cmd+Shift+P, search for Toggle Line Comment, and run it. If it works, the issue is with the keybinding, not the command itself.
Open keybindings.json with Cmd+Shift+P, then run Preferences: Open Keyboard Shortcuts JSON, and paste your entry for commentLine here. We need to make sure the command ID is set to editor.action.commentLine, and not something else.