Boox Color Series User Manual page 143

Split Screen
This supports Apps Split-Screen. You can select Split-Screen from the
system drop-down bar when an application is opened, and then select a
document, a notepad or other application that you want to open on the
other side of your screen.
The system interface does not support enabling Split-Screen directly.
You need to start an application before enabling it;
The applications that do not support Split-Screen will prompt "This
application does not support Split-Screen" when split screen is enabled;