You can still pull bobbin thread even though the hook shaft is stuck. That doesn't explain not being able to remove the bobbin case. The latch needs to be completely open. These tolerances are much closer than the typical old Singer.
Now remove the back part of the cover and the feed dogs for a better view.
Feed dog lever positions- there are 3. Totally up is the bobbin clutch. Nothing else turns in this position. Return to horizontal. Now try to spin handwheel.