The EOL (for qubes) will be announced here with a separate topic (you won’t miss that), when it’s ready to install. THEN you can install it with:
sudo qubes-dom0-update qubes-template-fedora-35
until that, you need to grab the 35 from the testing repos, with:
sudo qubes-dom0-update --enablerepo=qubes-templates-itl-testing qubes-template-fedora-35