What is this new button in Windows 11 Task View?

The circled tile is not another local virtual desktop. It is the Connect to Cloud PC entry used by Windows 365 Switch for a Cloud PC or dev box added from Windows App. That explains the external-arrow icon and why it appears beside Desktop 1 and New desktop. Open Windows App, sign in, choose Devices, and check whether a Cloud PC or dev box is listed. On its menu, select Remove from Task view, then add it again. Update Windows App and Windows first. If no remote device is assigned, the tile is stale; removing it will not delete a Cloud PC or affect local desktops. If the tile remains blank or unresponsive, repair or reinstall Windows App, then sign in again. Only one Switch-enabled Cloud PC is supported at a time. If this is a managed device, ask the Windows 365 administrator to confirm the assignment and service health.