I am using STM32L063C8T6 (LQFP-48).
So, USB_NOE is not available if you want to keep SWD active (highly recommended).
As said, this is not a big deal, and USB can be used with no problems.
Remember that CubeMX will always give warnings when some pin can not mapped.
The peripheral function can still be usable though, as in this case.
If some peripheral or function cannot possibly be configured (no alternative mapping for its essential pins), it'll appear in red.
Code can still be generated, for the other configured peripherals.