In August of 2018 Lenovo has joined the Linux Vendor Firmware Service (LVFS) project, which enables firmware updates from within the OS. BIOS updates (and possibly other firmware such as the Thunderbolt controller) can be queried for and installed through fwupd.
Lenovo may in the future provide cabinet files that can be directly installed with fwupdmgr. Check for Linux .cab files from the Lenovo ThinkPad X1 Carbon (Gen 8) driver website.
The BIOS has two Sleep State options, Windows and Linux, which you can find in at Config > Power > Sleep State. The Linux option is the traditional S3 power state where all hardware components are turned off except for the RAM, and it should work normally. The Windows option is a newer software-based "modern standby" which works on Linux (despite the name). One possible benefit to the Windows sleep state is faster wake up time, and one possible drawback is increased power usage.
See acpid#Enabling backlight control if the LCD brightness keys do not work by default.
Lenovo developers do not think NFC is a priority as of August 2020.