It seems that the either the Global Menu widget has not been ported to Plasma 6 or the necessary library has not been built with Qt6. I noticed that there is a package called libdbusmenu-qt5 in the repositories, which is installed, but there is not a libdbusmenu-qt6.

Also Active Window Control does not appear in a search for widgets in "Get New Widgets".

Can you shed some light on these issues and what can be done to fix them, if possible. The OCtopi sysinfo output is here.

Thank you for distributing a KaOS ISO with Plasma 6 for your fellow KDE fans who are excited to try it.

As you can see the libdbusmenu-qt is a dead project:
https://launchpad.net/libdbusmenu-qt
No commits since 2016, no Qt6 support unless heavily patched, this means it slated to be removed from the repo, once more Qt5 parts are removed.
It should have been merged into kf6, without the need to have libdbusmenu installed:
https://invent.kde.org/frameworks/knotifications/-/merge_requests/99#note_682406
EDIT:
So question is what doesn't work, just tested it now, added an empty panel, added the global menu widget to it, new opened apps show their menu in the panel.
Wdigets not showing, means they have not been added/ported to plasma-addons yet.