Cubase 13 out now!

[Jorge_Ruiz]

Judging by this thread, not very promising:

External Instrument Retains 'In Use' State When No Longer Used

When an Instrument track has been removed from a project, its status in The External Instruments tab often remains ‘In Use’, with an X in the “Used” column If you create a new Intrument track and try to select this External Instument, nothing happens, the selection is ignored and the Inspector setting stays “No VST Instrument”. Closing and restarting Cubase seems to free up this stale status. I’ve not found another way.