The dependency you are talking about is phonon-qt6-vlc. If you have mpv installed, you can redirect this dependency to phonon-qt6-mpv:
Uninstall VLC under Plasma 6 (dependency phonon-qt6-vlc):
=> Install phonon-qt6-mpv first: yay phonon-qt6-mpv
=> Then uninstall phonon-qt6-vlc: sudo pacman -R phonon-qt6-vlc
=> After you have uninstalled phonon-qt6-vlc, then uninstall vlc: sudo pacman -R vlc
=> Reboot
However, phonon-qt6-mpv is a package from the AUR, so install with yay.
Edit: However, there will still be vlc folders in your /home directory that you will have to delete manually.