I'm also confused, after some googling :
"The screen quality always was a sore point for many T series ThinkPads of the past. With the newest generation, Lenovo appears to be working on this weak-point, as all three Tx90 ThinkPads will be optionally offered with either QHD (2,560 x 1,440) or 4K-UHD (3,840 x 2,160) panels that offer a brightness of 500 nits. Lenovo is not only increasing the brightness of the most expensive screen options, they are also going to offer brighter FHD (1,920 x 1,080) options for both the T490 and the T490s with a brightness of up to 400 nits. There are two such options: A FHD panel with PrivacyGuard, Lenovo's ePrivacy solution, and a second 400 nits FHD panel that consumes less energy (Low Power FHD)."
I also don't see the option. Weird...