Since Start menu is back in Windows 10 which in its own form not optimized for tablet users, Microsoft decided to include a toggle switch using which one can easily switch to Tablet Mode from the Action Center.
Tablet Mode optimizes Windows 10 to be touch-friendly by maximizing all dialog box sizes and makes the start menu to be full screen like in Windows 8.1. But when you switch into Tablet mode, you will find that the app icons on the taskbar is missing including Microsoft Edge, Explorer, Store, any apps that you placed, and open apps. Microsoft thinks that this app shortcuts are not optimal for touch and hence are hidden by default settings.
However if you are used to opening apps from taskbar, you will find it frustrating and you may want the apps back on taskbar in Tablet mode too.
Go to Action Center and click on All settings. Select Tablet mode and toggle the switch Hide app icons on the taskbar in tablet mode to Off.
You will immediately see the icons back on Taskbar. Enjoy!