Comment 6 for bug 1977701

FYI to clarify - these were tested by enabling -proposed as per https://wiki.ubuntu.com/Testing/EnableProposed

# enable proposed so we can install intel-microcode from there
# https://wiki.ubuntu.com/Testing/EnableProposed

cat <<EOF | sudo tee /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

cat <<EOF | sudo tee /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

sudo apt update

Then installed as:

sudo apt install intel-microcode/$(lsb_release -cs)-proposed

And rebooted to test the machine boots correctly.