Dear @olf:

going through https://www.qt.io/product/features#js-6-3 (LGPLv3), I can see that Qt Wayland Compositor is not compatible with it and requires GPLv3 (or "commercial"). Lipstick runs on it, but fortunately it is open-source. Not sure of the rest of the composer.

Qt Wayland is also used by Flatpak UI, but that is open source.

LGPLv3 has Tivoization/DRM clauses (referred to in Qt FAQ) which maybe an issue for Jolla as well.