KDE neon unstable edition is built from git master. For the last few weeks we have frozen the published repo because we knew the move to Qt 6 based builds of KDE Frameworks and Plasma would break install. They will still break install but now is the time to give it a try. It is vitally important to update your neon-settings-2 package first because the Qt 5 and 6 builds have overlapping files and this will allow that.
pkcon refresh
pkcon install neon-settings-2
pkcon update
or if you prefer apt
apt update
apt install neon-settings-2
apt full-upgrade
This is very early stage development. Almost everything is super broken from a user perspective, and it may not be useful to get 500 bug reports about every little thing so tread carefully. For any bug reports you do report add `qt6` tag.
Best of luck!