I have a Dell Inspiron 13 5370 (non touchscreen version), running Ubuntu 18.04.3 LTS and kernel "Linux 5.4.1-050401-generic".
The keyboard back light won't work. The shortcut key Fn+F10 brings up the controls and cycles through the 3 levels (off, mid, full) but the keyboard backlights don't actually do anything. The only working light is the Caps lock LED indicator. This experience was replicated with Lubuntu and Manjaro LiveUSBs.
The keyboard backlight works fine with Windows 10 once the driver is installed from Dell's website.
Tested the change recommended in below link. It does not appear to make a difference I used the 100s recommended it did say 63h. Rechecked after change and it shows 1m as suggested in article however keyboard back light still appears to not be functioning. https://www.dell.com/support/article/uk/en/ukbsdt1/sln308123/how-to-configure-the-keyboard-backlight-time-out-interval-in-ubuntu-linux?lang=en