I tested the dist-upgrader tarball from -proposed and was able to upgrade with both ubuntu-desktop and lubuntu-desktop meta packages installed. Additionally, xscreensaver remained installed.
Relevant bits of /var/log/dist-upgrade/main.log 2020-07-21 09:02:44,309 INFO Using config files '['./DistUpgrade.cfg.bionic']' 2020-07-21 09:02:44,309 INFO uname information: 'Linux clean-bionic-amd64 4.15.0-112-generic #113-Ubuntu SMP Thu Jul 9 23:41:39 UTC 2020 x86_ 64' 2020-07-21 09:02:44,728 INFO apt version: '1.6.12ubuntu0.1' 2020-07-21 09:02:44,728 INFO python version: '3.6.9 (default, Apr 18 2020, 01:56:04) [GCC 8.4.0]' 2020-07-21 09:02:44,732 INFO release-upgrader version '20.04.23' started ... 2020-07-21 09:06:09,648 DEBUG Marking 'ubuntu-desktop' for upgrade 2020-07-21 09:06:09,682 DEBUG Marking 'lubuntu-desktop' for upgrade 2020-07-21 09:06:10,125 DEBUG About to apply the following changes bdmurray@clean-bionic-amd64:/tmp/focal$ apt-cache policy xscreensaver xscreensaver: Installed: 5.42+dfsg1-1ubuntu1 Candidate: 5.42+dfsg1-1ubuntu1 Version table: *** 5.42+dfsg1-1ubuntu1 500 500 http://192.168.10.7/ubuntu focal/universe amd64 Packages 100 /var/lib/dpkg/status ** Tags removed: verification-needed-focal ** Tags added: verification-done-focal -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1875107 Title: unable to upgrade with lubuntu-desktop and ubuntu-desktop installed due to xscreensaver To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/ubuntu-release-upgrader/+bug/1875107/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs