Qt 6.0 betas and rc have been in the kde-next repository for the last 4-6 weeks. Yesterday the first stable version was released, Qt 6.0.0 and is now available in the regular, stable repositories.
Not many are ready for it though, internal tools like qmlscene-qt6 and qtdesigner-qt6 have worked all along, but today the first regular app was ported to Qt 6, Strawberry. Builds and runs fine, so far no regressions seen compared to a Qt 5 build.

A second application running on Qt 6, KaOS' own Notepad (simple text editor, created because of a missing editor during the early Qt 5 transition). So it might be a handy simple app again with another Qt transition.

8 days later

Three more applications are ready for Qt 6, added is qtkeychain-qt6 (Qt 5 version needs to stay default for now).
Qjackctl & Qsynth 0.9.0 are both build with Qt 6, no issues:

9 months later

There wasn't much to report for the Qt 6.1 series, not very usable, very incomplete, but that has now changed with Qt 6.2.
Many more are ported from Qt5,, that includes qt6-location and the big one, qt6-webengine (plus all the Qt6 webengine depends on).
For this reason, 6.2.0 RC1 has been made available to all users. Normally an rc won't be in the stable repos, but 6.2 (rc) is far more usable then stable 6.1.3.
Example QML web browser build with Qt 6.2.0rc1 webengine:

3 months later

The PyQT stack is now mostly QT6 ready too, first app that uses it is Eric(7):

Eric7 will replace Eric6 on update for now, there are conflicting files, so both can't be installed at the same time, if too many issues, then the replace will be removed, just a conflict left then. But there shouldn't be any real problems.

16 days later

With the release of Kvantum 1.0.0, it is now also possible to have Kvantum style for Qt 6 apps. It is not automatically installed yet, package name is kvantum-qt6 for now, add it to your install if you already use some Qt6 apps and want good integration.

    18 days later

    Qbittorrent is the next application ready for Qt6:

    2 months later

    It is rather slow going, but one more is ready for Qt6, rssguard:

    3 months later

    Focuswriter is the latest application ported to Qt6 (with version 1.8.0)

    17 days later

    MKVToolNix 69.0.0 also ported to Qt6

    22 days later

    The pace of moving to Qt6 seems to be picking up, now Avidemux is also Qt6:

    a month later

    Obs-studio (only real option so far to do desktop recording on Wayland) has moved to Qt6 with 28.0.0:

    15 days later