We’ve observed that some older QTS versions might encounter the issue described in this FAQ:
VM console shows black screen in Virtualization Station 4.0.0.278 - Fixed in QTS 5.2.4 | QNAP
If you’re already on the latest QTS version and still facing problems, please try connecting directly using your NAS’s local IP address (e.g., 192.168.x.x). This can help us rule out any potential impact from your network or router.
Let us know if this helps!