It looks like this PR deleted every puppet upgrade doc since 3.3. Looking at the commit messages, this was done intentionally. I have no clue why though. Nevertheless, the last version before deletion still mentioned Puppet 4.
According to the Foreman docs Puppet 5 is supported and I guess it has been for quite some time now. Puppet 6 support is still not finished afaik. I would guess this is both true for Foreman, too.
Exactly what I thought.
Still, the old docs should still remain where they were in my opinion or at least the menu entry should be removed. Having internal links in the doc that 404 does not look to good (and obviously confuses people).
If you look at the details then 3.7 and 3.8 automatically resets --puppet-server-puppetserver-version. 3.9 and 3.10 added --puppet-server-puppetserver-metrics while 3.11 fixes the root cause by never storing any value for this. It also correctly handles --puppet-server-jvm-extra-args.
On the Foreman side we’re still lacking support for reinstalling puppet-agent-oauth if needed. Once we add that we’ll always be able to just handle what’s present, whether that’s Puppet 4, 5 or (hopefully soon) 6.