The Lenovo X1 Carbon 6th gen is quite a nice laptop overall. It used to have some quirks under Linux, with regards to ACPI sleep, CPU frequency and such. They have all been taken care of by BIOS upgrades, already, so just upgrade if you any issues there.
There was one thing that I never got properly to work: Bluetooth. The new 6th gen uses a different chipset than the older models which I saw working just fine on my colleagues machines. It turns out, that the new chipset also did work fine under old Kernels (I tested 4.9) while on newer ones (I tested 4.16 and 4.18) it's just behaving weirdly. Sometimes it might find devices, sometimes it might pair, sometimes it might work for a couple of seconds, but mostly it will not work.
After some time researching the issue, because I didn't want to run a 2 year old kernel if I didn't have to, I found this discussion on Launchpad: https://bugs.launchpad.net/ubuntu/+source/linux-firmware/+bug/1729389
Turns out, the Intel developers know about the problem and it's already fixed in some downstreams of the kernel. If it isn't working for your Distro of choice, you can just change one setting in the kernel module. Add this one line to your
options iwlwifi bt_coex_active=0
Create the file if it isn't already there (it wasn't for me on Debian Testing). Reboot and check if the
bt_coex option is disabled:
cat /sys/module/iwlwifi/parameters/bt_coex_active N
If you're curious what the flag is about, you can read a good explanation on Superuser.com.
You're good to go now. Enjoy all the BT goodness of Audio, input devices and so forth.