Hello,
I'm not sure I understand the issue.
Do you have something on the screen of your Lenovo Pro dock?
If you have mirroring, that is normal default behaviour. Windows 10, on laptops, is designed to clone to the first external display and extend to followings. Rebooting doesn't change settings.
You
simply right click on the desktop, select display settings, select extend desktop.
The settings is then saved and will persist across reboots.
If it's different, I would need more details to understand.
Kind regards,
Alban