You can still deny devices access to your network

You can still deny devices access to your network in the "new" list-based user interface. On dashboard, click Devices, then click the right arrow to right of the active device you want to block. That opens that device's details window. Click the pause button (=) at the upper right of the device details window to temporarily block access. The pause button changes to a play button ( ▶️ ). Press that to allow access if you change your mind. To permanently deny access you'll need to delete the device's profile from the app. Click red text "delete this device" at bottom of the device's details page. However if that device has your network password stored on it, you'll need to delete or "forget" the wifi profile on the device itself or change your network password.