You can install stable version: AUR.
theShell has a super unstable untested version called "blueprint" which can be installed with AUR.
Use ts-startsession in an X session to start theShell. Or use a display manager and use "theShell" as the session.
Pressing the "Adjust Screen Resolution" nothing happens...
Make sure KScreen and the KDE CLI tools are installed.
For more questions, see theshell issues.
Use a different window manager
In theShell settings, under the "Danger" category, enter the command to start the window manager in "Window Manager Command".
Tips and tricks
Stable version installed with "blueprint" version
theShell and theShell Blueprint can be installed together. Just rename the binary and initialization script (a good name is theshell-b and init-theshell-b), put them in your binaries folder, rename the .desktop file, change it to start the new initialization script and put it in your xsessions folder.