@vaclav ThinkPad T480 and T480s are both supported. Please read:
https://libreboot.org/docs/install/t480.html
Please note that they use different build targets in Libreboot, so you should make sure to choose the right ROM image.
The discrete Nvidia graphics are unsupported. Machines that have it, also have Intel graphics, and Libreboot configures all such machines to use only the Intel graphics. Errata is documented on that page.
Keep that in mind when flashing. Libreboot only configures the Intel GPU.