Is there any particular distro you're using KDE on for this to work flawlessly on a Thinkpad? I have a Carbon Gen 6 on Windows 10 but one day will need to migrate. The device itself is sound and reliable.
fedora / fedora immutable (the aurora project under the universalblue umbrella has a really nice batteries included setup).
Fingerprint reader, backlight, etc, everything works (at least for my thinkpads). I think any recent model everything should work out of the box.