Deja Dup`s "Back Up Now" button is not highlighted
Shorter version
Ctrl+Alt+t to open a terminal
pkill deja-dup
Re-run the "Backups" program and try again.
In my case, there was no backup running but deja-dup had a couple of things running.
I did a ps -eaf | grep dup
and killed the pids. Then I started DejaDup from the menu and the button was active.
That button is grayed out when a backup (or restore) is already in progress. Maybe one was running in the background?
Is the button enabled now?