Cannot boot after upgrade from Trisquel 10 to 11

Did you have Trisquel installed with encrypted boot? I.e. you had to type a passphrase from the very begining? I had that before on my X200 but I can't remember how it exactly looked like.

Just some updates:
I have booted the Trisquel 11 Live ISO and it seems to work fine with my laptop. So it doesn't seem to be a general Trisquel 11 issue.
I have zero to limited experience in troubleshooting system logs. But I looked at the syslog file and found these entries at the end:

May 27 18:13:02 martin-ThinkPad-X200 xdg-desktop-por[1502]: xdg-desktop-portal-gtk: Fatal IO error 11 (Die Ressource ist zur Zeit nicht verfügbar) on X server :0.
May 27 18:13:02 martin-ThinkPad-X200 systemd[1]: Stopping Dispatcher daemon for systemd-networkd...
May 27 18:13:02 martin-ThinkPad-X200 ntpd[78296]: ntpd exiting on signal 15 (Terminated)
May 27 18:13:02 martin-ThinkPad-X200 systemd[1]: Stopping Network Time Service...
May 27 18:13:02 martin-ThinkPad-X200 ntpd[78296]: 192.168.178.1 local addr 192.168.178.77 ->
May 27 18:13:02 martin-ThinkPad-X200 systemd[1]: Stopping Telephony service...
May 27 18:13:02 martin-ThinkPad-X200 ofonod[62809]: Terminating
May 27 18:13:02 martin-ThinkPad-X200 systemd[1]: Stopping LSB: Set the CPU Frequency Scaling governor to "ondemand"...
May 27 18:13:02 martin-ThinkPad-X200 bluetoothd[72735]: Stopping SDP server
May 27 18:13:02 martin-ThinkPad-X200 systemd[1]: openvpn.service: Deactivated successfully.
May 27 18:13:02 martin-ThinkPad-X200 bluetoothd[72735]: Exit
May 27 18:13:02 martin-ThinkPad-X200 systemd[1]: Stopped OpenVPN service.
May 27 18:13:02 martin-ThinkPad-X200 systemd[1252]: xdg-desktop-portal-gtk.service: Main process exited, code=exited, status=1/FAILURE
May 27 18:13:02 martin-ThinkPad-X200 systemd[1252]: xdg-desktop-portal-gtk.service: Failed with result 'exit-code'.
May 27 18:13:02 martin-ThinkPad-X200 systemd[1]: Stopping PackageKit Daemon...
May 27 18:13:02 martin-ThinkPad-X200 systemd[1]: Stopping Power Profiles daemon...
May 27 18:13:02 martin-ThinkPad-X200 dundee[62799]: Exit
May 27 18:13:02 martin-ThinkPad-X200 systemd[1]: Stopping LSB: Run /etc/rc.local if it exist...

Not entirely sure how to interpret this, but there seems to be some issue with starting the desktop environment?
Again, any help here highly appreciated. I can also provide full/more logs, if needed.

These log entries look like a system switching off while you mentioned that boot wasn't successful. Since you see the GRUB background, I don't know whether GRUB started booting linux at all. If so, it would be possible to look for logs.

However, reinstalling Trisquel might be easier. If you have a separate home partition, you can select the option to keep it (but better to have a backup in case of mistake). You can also do a backup of /home and /etc to an external disk (/etc is only useful if you modified something there) with BackInTime, do a default install from the live USB and restore /home.

One more thing that would be useful is to save the list of installed packages so that you can reinstall them all at once. I normally save and restore the list with synaptic but in your case that is not possible since you cannot boot your system. I guess it may be possible to boot on the live USB, mount your disk, chroot to it, and save the output of "apt list --installed | grep '/' | cut -d'/' -f1" (the number of packages it gives for me is exactly the same like synaptic) but I am not sure what is the proper way to install the packages from that list.

Perhaps someone has the answer to that.

Thanks, Avron and Magic Banana, for your valuable hints and sorry for my late reply. In fact I decided to do a re-install.