In the strange bouillabaisse that is Windows 8.1 Update 1, nothing is stranger, perhaps, that accessing desktop user interfaces from within Modern apps and experiences. In the RTM version of this update, I've been experimenting with how these cross-experience UIs work. And one of the weirder ones is the ability to access the taskbar from inside Modern apps.
As with the Modern app taskbar preview capabilities I discussed in Windows 8.1 Update 1: Modern App Taskbar Previews, this functionality is of course designed to bridge the conceptual and usability gulfs that currently exist in Windows 8.1. It's supposed to make Windows 8.1 work better for those of us who still use traditional, non-touch PCs, and do so without changing the experience for those with multi-touch tablets and 2-in-1 Pcs.
As such, your PC(s) may not be configured properly to display the taskbar in Modern apps, a fact that several readers and people on Twitter were able to help me with. In my initial tests of the RTM version of Update 1—which I've installed on all my PCs, including my desktop and Ultrabook, my Surface devices, my mini-tablets and even in VMs—I was seeing inconsistent results. And with different sign-ins, too, since I started to suspect that some kind of setting was being synced through my Microsoft accounts.
Turns out this was in effect correct, but I just didn't know which setting was being synced. Now I do: In order to see the taskbar in Modern apps, you have to be displaying all running Modern apps on the taskbar first. This is enabled by selecting the option "Show Windows Store apps on the taskbar" in the Taskbar pane of the Taskbar and Navigation Properties window.
Now, when you use a Modern app, you can mouse down to the bottom of the screen and the taskbar will appear so you can switch apps using the interface you're already familiar with.
Using touch? Don't worry about it. You'll never see this interface regardless.