Comment 15 for bug 1969976

Aaron:

This step adds the repository to apt:

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

This step makes it so that packages from -proposes are not automatically pulled in, which is what you want:

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

Then to install the fwupd package in particular:

sudo apt-get install fwupd/jammy-proposed

I hope this helps. If not maybe try #ubuntu on Libera IRC.