Notepad++ is a Windows application.
Ones that are easily accessible on Ubuntu are running in a Wine or similar environment, and are unofficial distributions.
So if you have that environment, you may be able to manually download the ARM version that @terry-r mentioned and get it to run. And maybe whoever supplies the easy-to-install bundle for Ubuntu might choose to eventually distribute one for ARM Ubuntu as well.
But Notepad++ developers do not support it running on any non-Windows environment, and do not and will not supply bundles for non-Windows environments