I confirm the same behaviour on Linux Debian 9 + Apache 2.4.25 + PHP 7.0.33 + MariaDB 10.1.41 (all debian packages updated to latest version)
My installation actually was pre-existing, and it stopped working on 01/01/2020
No automated action was done, apart from standard security packages upgrades when required.
No automated action was scheduled for that time, GroupOffice just stopped working, I suppose because of packages upgrades.
Then I both tried upgrades with existing database and fresh new installs with empty database, but they both failed.
There are no errors in the logs, the software keep falling back to the installation page.
Using Group Office since may years, I had to stop because of this and fall back to another email client.