qt was stuck with 5.15 because the telegram app depended on it (sigh). Had to do a dnf upgrade --best --allowerasing for the update to qt6 (and the removal of telegram lol).
Yeah i know, i just prefer to use the distros native package manager. That said, i use the jellyfin client from flathub and that one now warns me as well that it depends on qt5.15 (works fine though, since flatpak can have multiple versions of dependencies).