If you find that windows 10 taskbar not hiding then you can always try restarting your computer and see if the problem still exists. If it does, then click on the notification area icon and most of the time, just clicking on this button gets you rid of the problem. If these two steps do not help you out, then let me know. See the solution here https://appuals.com/taskbar-refuses-to-auto-hide-in-windows-10/ as well.