For the record, I did close the window. I don't use Deja Dup for my backups, so in a way, you're right.
Deja Dup is actually a front-end to duplicity. I don't know the technical details of how daily/weekly backups are scheduled, or what is responsible for the showing prompt. There is a process that's supposed to start at login and run in the background ("Backup Monitor" / deja-cup-monitor)
Thank you. Perhaps this is the problem. I will go check of this background process runs if I reboot and report back.
If you don't mind a slightly off topic question, what do you use for your backups?
I checked and htop shows there is no deja-dup-monitor running.
In startup applications there is a /usr/libexec/deja-dup/deja-dup-monitor that is supposed to run but it does not run.
I will increase the delay to 15 seconds and see if that makes it run or not and reboot and report back.
P
I changed it to 15 seconds startup but still /usr/libexec/deja-dup/deja-dup-monitor in the startup applications does not start.
Does it start for you on 20.04 you downloaded if you reboot?
How could I ascertain why it does not start?
Thanks in advance,
P
I found more on the issue here:
Also if I type in a terminal:
cat /var/log/syslog | grep org.gnome.DejaDup.Monitor
Mar 11 14:39:24 aragorn mate-session[2856]: WARNING: Could not parse desktop file /etc/xdg/autostart/org.gnome.DejaDup.Monitor.desktop: Unrecognized desktop file Version '1.1'
Mar 11 14:39:24 aragorn mate-session[2856]: WARNING: could not read /etc/xdg/autostart/org.gnome.DejaDup.Monitor.desktop
Mar 11 14:51:14 aragorn mate-session[2746]: WARNING: Could not parse desktop file /etc/xdg/autostart/org.gnome.DejaDup.Monitor.desktop: Unrecognized desktop file Version '1.1'
Mar 11 14:51:14 aragorn mate-session[2746]: WARNING: could not read /etc/xdg/autostart/org.gnome.DejaDup.Monitor.desktop
Mar 11 14:57:01 aragorn mate-session[2747]: WARNING: Could not parse desktop file /home/aragorn/.config/autostart/org.gnome.DejaDup.Monitor.desktop: Unrecognized desktop file Version '1.1'
Mar 11 14:57:01 aragorn mate-session[2747]: WARNING: could not read /home/aragorn/.config/autostart/org.gnome.DejaDup.Monitor.desktop
Mar 11 14:57:01 aragorn mate-session[2747]: WARNING: Could not parse desktop file /etc/xdg/autostart/org.gnome.DejaDup.Monitor.desktop: Unrecognized desktop file Version '1.1'
Mar 11 14:57:01 aragorn mate-session[2747]: WARNING: could not read /etc/xdg/autostart/org.gnome.DejaDup.Monitor.desktop
So i have same issue. Looks like a MATE problem specifically?
I created a shell script for a dedicated backup USB drive which runs rsync on my 2 data drives. It's interactive, so I dry run first and evaluate everything that's changed. Before that, I run a different script to clean up junk (usually cache folders and certain log files).
For snapshotting the OS and applications, I literally tar up the system. That does mean in event of a disk failure, I'd have to manually re-create partitions and re-install the bootloader, but I'm comfortable with that.
Previously I used Clonezilla for snapshots, but I found it clumbersome for extracting a few files.
I can confirm that it's not launching for me either in 20.04. It does launch if I place the command into a shell script (.sh) and add that to Start-up Applications.
The removal of this line also works.
Version=1.1
So yes, a bug in MATE. Very good findings, thank you. 
I'll create an issue on mate-session-manager a bit later 
... (unless I'm beaten to it)
If it isn't released in time, a possible alternate is for someone at Canonical to patch the deja-dup package. 
OMG I really hope this can be fixed before launch because otherwise people could complain MATE lost all their PC and is bad when its actually really good so I will try my best to log a ticket there on the link you posted and beg a fix is added.
I added a bug here:
Thanks for help @lah7 and @franksmcb .
P
I was posting an issue at the same time. 
No problem, can I ask is there a chance we can fix this before 20.04 ships so that its not a problem for many many users?
I am fairly confident this will be resolved in some fashion prior to the official 20.04 release.
Good news! Our project leader has committed a patch so this issue will be no more in an upcoming daily ISO. 
This has been fixed in mate-session-manager 1.24.0-2ubuntu1
Thats great so if I update now it is fixed?
Yes, 1.24.0-2ubuntu1 was published for 20.04.
Just for reference: Any non-Ubuntu users coming to this topic should observe the fix was a patch at a package-level in Ubuntu. Debian, for example doesn't have the patch.
To fully fix this, MATE Session Manager (aka. upstream) still need to make changes to the code to properly address the issue - that is, if there is more to do then a simple one line change:
Im so glad this got fixed because it was really worrying me.