You need to be able to modify the DMVT Pre-alloc size of the memory card in your BIOS to 96 MB or higher in order to drive a QHD+ screen.
This is because the OS X driver works differently with the Intel HD graphics compared to the Windows driver.
If you do not have that option in your BIOS, you are out of luck.
On the Dell XPS I had to unlock the BIOS to get this option, however BIOS unlocking is dangerous and
can brick your laptop.
Additionally Lenovo laptops are heavily protected against BIOS unlocking, so best ask questions about that on a dedicated BIOS unlocking forum.