Comment 8 for bug 2048529

Here is what happens when taking the default except where just hitting enter would abort the upgrade.
Logging all decisions (except the do you really want to do that inside ssh)

...

Xenial -> Bionic

3 installed packages are no longer supported by Canonical. You can
still get support from the community.

4 packages are going to be removed. 227 new packages are going to be
installed. 436 packages are going to be upgraded.

You have to download a total of 350 M. This download will take about
1 minute with your connection.

Installing the upgrade can take several hours. Once the download has
finished, the process cannot be canceled.

 Continue [yN] Details [d]
y

39 packages are going to be removed.

 Continue [yN] Details [d]d

...

Remove: initscripts insserv libbind9-140 libcryptsetup4
  libdns-export162 libdns162 libevent-2.0-5 libgdbm3 libicu55
  libisc-export160 libisc160 libisccc140 libisccfg140 libjson-c2
  liblwres141 libmpfr4 libpng12-0 libprocps4 libpython3.5-minimal
  libpython3.5-stdlib libreadline6 libxtables11 python3.5
  python3.5-minimal sysv-rc

Remove (was auto installed) cgmanager libboost-iostreams1.58.0
  libboost-random1.58.0 libboost-system1.58.0 libboost-thread1.58.0
  libcgmanager0 libnih-dbus1 libpython3.5 libx86-1 libxen-4.6
  linux-headers-4.4.0-210 linux-headers-4.4.0-210-generic pm-utils
  vbetool

Continue [yN] Details [d]
N

Restart required
(has to be done to be able to enter the next upgrade)
Continue [yN]
Y

---

# Now Bionic to Focal

16 installed packages are no longer supported by Canonical. You can
still get support from the community.

3 packages are going to be removed. 195 new packages are going to be
installed. 603 packages are going to be upgraded.

You have to download a total of 453 M. This download will take about
1 minute with your connection.

Installing the upgrade can take several hours. Once the download has
finished, the process cannot be canceled.

 Continue [yN] Details [d]

Remove: btrfs-tools command-not-found-data gcc-5-base gcc-6-base
  libffi6 libhogweed4 liblvm2app2.2 liblvm2cmd2.02 libnettle6 libnih1
  libplymouth4 libvirt-bin ureadahead

Remove (was auto installed) augeas-lenses bridge-utils cgmanager
  ebtables efibootmgr gcc-8-base libargon2-0 libaugeas0 libbind9-160
  libbluetooth3 libboost-iostreams1.58.0 libboost-random1.58.0
  libboost-system1.58.0 libboost-thread1.58.0 libbrlapi0.6
  libcgmanager0 libdns-export1100 libdns1100 libevent-2.1-6 libgdbm5
  libicu60 libip4tc0 libip6tc0 libiptc0 libirs160 libisc-export169
  libisc169 libisccc160 libisccfg160 libjson-c3 liblwres160 libnetcf1
  libnih-dbus1 libntfs-3g88 libperl5.26 libprocps6 libpython3.5
  libpython3.6 libpython3.6-minimal libpython3.6-stdlib libreadline7
  libsdl1.2debian libvpx5 libx86-1 libxen-4.6 libxen-4.9
  libxenstore3.0 libxentoolcore1 linux-headers-4.15.0-213
  linux-headers-4.15.0-213-generic linux-headers-4.4.0-210
  linux-headers-4.4.0-210-generic linux-image-4.4.0-210-generic
  linux-modules-4.4.0-210-generic nplan perl-modules-5.26 pm-utils
  python3-asn1crypto python3-pam python3.6 python3.6-minimal vbetool
  xdelta3

Continue [yN] Details [d]
N

Restart required
Continue [yN]
y

$ apt-cache policy libvirt-bin libvirt-clients; virsh -v
libvirt-bin:
  Installed: 4.0.0-1ubuntu8.21
  Candidate: 4.0.0-1ubuntu8.21
  Version table:
 *** 4.0.0-1ubuntu8.21 100
        100 /var/lib/dpkg/status
libvirt-clients:
  Installed: 6.0.0-0ubuntu8.16
  Candidate: 6.0.0-0ubuntu8.16
  Version table:
 *** 6.0.0-0ubuntu8.16 500
        500 http://archive.ubuntu.com/ubuntu focal-updates/main amd64 Packages
        500 http://security.ubuntu.com/ubuntu focal-security/main amd64 Packages
        100 /var/lib/dpkg/status
     6.0.0-0ubuntu8 500
        500 http://archive.ubuntu.com/ubuntu focal/main amd64 Packages
6.0.0

# Now Focal to Jammy

13 installed packages are no longer supported by Canonical. You can
still get support from the community.

10 packages are going to be removed. 146 new packages are going to be
installed. 757 packages are going to be upgraded.

You have to download a total of 691 M. This download will take about
2 minutes with your connection.

Installing the upgrade can take several hours. Once the download has
finished, the process cannot be canceled.

 Continue [yN] Details [d]
y

Remove obsolete packages?

120 packages are going to be removed.

Removing the packages can take several hours.

 Continue [yN] Details [d]d

Remove: e2fslibs fonts-ubuntu-font-family-console libcomerr2
  libfwupdplugin1 libidn11 libldap-2.4-2 libreadline5 libsepol1 lxd
  lxd-client

Remove (was auto installed) augeas-lenses bridge-utils cgmanager crda
  cryptsetup-run ebtables efibootmgr gcc-10-base gcc-8-base
  libargon2-0 libaugeas0 libbind9-160 libbluetooth3
  libboost-iostreams1.58.0 libboost-iostreams1.71.0
  libboost-random1.58.0 libboost-system1.58.0 libboost-thread1.58.0
  libboost-thread1.71.0 libbrlapi0.6 libbrlapi0.7 libcanberra0
  libcbor0.6 libcgmanager0 libdns-export1100 libdns-export1109
  libdns1100 libevent-2.1-6 libevent-2.1-7 libffi7 libfl2 libgdbm5
  libgdk-pixbuf-xlib-2.0-0 libgdk-pixbuf2.0-0 libhogweed5 libicu60
  libicu66 libip4tc0 libip6tc0 libiptc0 libirs160 libisc-export169
  libisc169 libisccc160 libisccfg160 libjson-c3 libjson-c4 libltdl7
  liblwres160 libnetcf1 libnettle7 libnih-dbus1 libntfs-3g88
  libntfs-3g883 libperl5.30 libprocps6 libpython3.5 libpython3.6
  libpython3.6-minimal libpython3.6-stdlib libpython3.8
  libpython3.8-minimal libpython3.8-stdlib libreadline7 librest-0.7-0
  libsdl1.2debian libsoup-gnome2.4-1 libssl1.1 libtdb1 liburcu6
  libvirt-daemon-driver-storage-rbd libvorbisfile3 libvpx5 libvpx6
  libwebp6 libx86-1 libxen-4.6 libxen-4.9 libxenstore3.0
  libxentoolcore1 libxmlb1 linux-headers-4.15.0-213
  linux-headers-4.15.0-213-generic linux-headers-4.4.0-210
  linux-headers-4.4.0-210-generic linux-headers-5.4.0-169
  linux-headers-5.4.0-169-generic linux-image-4.15.0-213-generic
  linux-image-4.4.0-210-generic linux-modules-4.15.0-213-generic
  linux-modules-4.4.0-210-generic
  linux-modules-extra-4.15.0-213-generic
  linux-modules-extra-5.4.0-169-generic lz4 nplan perl-modules-5.30
  pm-utils python3-asn1crypto python3-entrypoints python3-pam
  python3-requests-unixsocket python3-simplejson python3.6
  python3.6-minimal python3.8 python3.8-minimal sharutils
  sound-theme-freedesktop vbetool xdelta3

Continue [yN] Details [d]
N

Restart required
Continue [yN]
y

$ apt-cache policy libvirt-bin libvirt-clients; virsh -v
libvirt-bin:
  Installed: 4.0.0-1ubuntu8.21
  Candidate: 4.0.0-1ubuntu8.21
  Version table:
 *** 4.0.0-1ubuntu8.21 100
        100 /var/lib/dpkg/status
libvirt-clients:
  Installed: 8.0.0-1ubuntu7.8
  Candidate: 8.0.0-1ubuntu7.8
  Version table:
 *** 8.0.0-1ubuntu7.8 500 (phased 10%)
        500 http://archive.ubuntu.com/ubuntu jammy-updates/main amd64 Packages
        100 /var/lib/dpkg/status
     8.0.0-1ubuntu7.5 500
        500 http://security.ubuntu.com/ubuntu jammy-security/main amd64 Packages
     8.0.0-1ubuntu7 500
        500 http://archive.ubuntu.com/ubuntu jammy/main amd64 Packages
8.0.0

So, if paying attention and saying "no" there, it actually is just fine.