Comment 5 for bug 1902469

I can confirm the kernel in groovy-proposed fixes this issue:

# enable proposed
cat <<EOF >/etc/apt/sources.list.d/ubuntu-$(lsb_release -cs)-proposed.list
# Enable Ubuntu proposed archive
deb http://archive.ubuntu.com/ubuntu/ $(lsb_release -cs)-proposed restricted main multiverse universe
EOF

# pin so packages are not automatically upgraded from -proposed
cat <<EOF >/etc/apt/preferences.d/proposed-updates
# Configure apt to allow selective installs of packages from proposed
Package: *
Pin: release a=$(lsb_release -cs)-proposed
Pin-Priority: 400
EOF

# install kernel from proposed
apt install linux-generic-hwe-20.04/groovy-proposed linux-headers-generic-hwe-20.04/groovy-proposed

# ensure "quiet splash" is still set in /etc/default/grub
grep quiet\ splash /etc/default/grub

reboot

# then I notice boot does not hang anymore with thunderbolt dock connected - \o/