Comment 6 for bug 1875107

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