better feature blocking

Author: devjiwonchoi

packages/next/src/next-devtools/dev-overlay/dev-overlay.tsx

@@ -47,7 +47,8 @@ export function DevOverlay({
                 />
               )}
 
-              {state.isDevToolsPanelOpen && <DevToolsPanel />}
+              {process.env.__NEXT_DEVTOOL_NEW_PANEL_UI &&
+                state.isDevToolsPanelOpen && <DevToolsPanel />}
 
               <ErrorOverlay
                 state={state}