I tested all available platforms:
offscreen, kms, linuxfb, minimal:
Qt Code: 
  1. (myApp:22797): Gtk-WARNING **: cannot open display: :0
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kms:
Qt Code: 
  1. pci id for fd 7: 80ee:beef, driver (null)
  2. No protocol specified
  3. pci id for fd 7: 80ee:beef, driver (null)
  4. No protocol specified
  5. pci id for fd 9: 80ee:beef, driver (null)
  6. pci id for fd 9: 80ee:beef, driver (null)
  7. No protocol specified
  8. pci id for fd 9: 80ee:beef, driver (null)
  9. No protocol specified
  10. pci id for fd 10: 80ee:beef, driver (null)
  11. pci id for fd 10: 80ee:beef, driver (null)
  12. No protocol specified
  13. pci id for fd 10: 80ee:beef, driver (null)
  14. No protocol specified
  15. pci id for fd 11: 80ee:beef, driver (null)
  16. pci id for fd 11: 80ee:beef, driver (null)
  17. No protocol specified
  18. pci id for fd 11: 80ee:beef, driver (null)
  19. 08:42:58.322 [Warning] Could not initialize EGL display
  20. 08:42:58.322 [Error] EGL error
  21. Aborted (core dumped)
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xcb:
Qt Code: 
  1. No protocol specified
  2. 08:44:35.494 [Error] QXcbConnection: Could not connect to display :0
  3. Aborted (core dumped)
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