GitLab 14 is not released for xenial. Upstream support for xenial ended in April, and 13.12 (the .0 version released 22 May) was the last GitLab version released for xenial, and they have mentioned that under “Deprecations” in several (I think) of the past release announcements.
You should get yourself on a newer Ubuntu version.
I updated Ubuntu and updated Gitlab again, but still couldn’t do it.
What other possible causes could there be?
ubuntu@ip-192-168-0-227:~$ lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 20.04.2 LTS
Release: 20.04
Codename: focal
ubuntu@ip-192-168-0-227:~$ sudo apt-get install gitlab-ce
Reading package lists... Done
Building dependency tree
Reading state information... Done
gitlab-ce is already the newest version (13.12.5-ce.0).
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
it should then pick up the new version. Yours will be slightly different, since the repo is for Ubuntu 18.04, but now you need to get the Ubuntu 20.04 one, so this should help.
Alternatively, you may need to go into /etc/apt/sources.list.d and remove the existing gitlab.list file and then run the curl command above. But only try this, if it fails from what I posted above.
I was able to update successfully.
Thanks to @iwalker and @grove for their help.
Very quick reply and solved the problem right away.
Thank you very much.