It looks like this is a pretty old thread, but your issue may have something to do with recent updates that landed in GNOME, which were released to Ubuntu about a week ago. More information on that can be seen here:
With regard to the error message, your system is nudging you to investigate a windowing system issue between the newer Wayland, vs. legacy X11. Have you tried running Picard over either protocol?
e.g., from the command line:
export QT_QPA_PLATFORM=xcb
, followed by picard
—or—
export QT_QPA_PLATFORM=wayland
followed by picard
?
If so, were there any error messages, or did the application load successfully between the two systems?
QMediaPlayer is the Qt class that allows the player at the bottom of Picard. This lets you preview tracks that are loaded into Picard.