Comment 14 for bug 1903776

I verified landscape-client 19.12-0ubuntu4.3 from focal-proposed.
I used landscape-server-quickstart from ppa:landscape/19.10 and registered the proposed client against it.
Then I had to enable the upcoming upgrade tool to the server:

# sudo -u landscape psql landscape-standalone-main -c "insert into meta_release (code_name, name, version, date, supported, upgrade_tool_tarball_url, upgrade_tool_signature_url, lts) VALUES ('jammy', 'Jammy Jellyfish', '22.04 LTS', now(), 't', 'http://archive.ubuntu.com/ubuntu/dists/jammy/main/dist-upgrader-all/current/jammy.tar.gz', 'http://archive.ubuntu.com/ubuntu/dists/jammy/main/dist-upgrader-all/current/jammy.tar.gz.gpg', 't')"
# sudo -u landscape psql landscape-standalone-main -c "update meta_release set upgrade_id=(select id from meta_release where code_name='jammy') where code_name in ('focal', 'impish')"

Launching the release upgrade activity from the web UI, the client machine was able to download and validate the upgrade tool and upgraded to jammy succesfully.