Hello,
FN+F5 and FN+F6 keys to adjust brightness don't work and can't be mapped.
Saw several problems for this here: One, two. But unfortunately it didn't solve my problem (or I missed something).

I installed Solus yesterday on my UEFI-configured Thinkpad T460s. FN+F1 - F4 (mute volume, lower volume, raise volume, mute mic) work like a charm, the rest don't. Biggest problem for me: the brightness keys. Also adjusting the brightness in the energy-options doesn't affect anything.
Installed xbacklight: Works via terminal.
Try to set custom shortcut via official keyboard-settings: No way. Just recognizes the (single) FN-key, not the XF86MonBrightnessUp/Down.
Try to adjust custom shortcut via dconf-editor: I'm able to set XF86MonBrightnessUp/Down-key manually, but it doesn't work.
Did add acpi_backlight=none to /etc/kernel/cmdline => nothing.
Did add acpi_osi=Linux to /etc/kernel/cmdline => nothing.

Also when I adjust brightness via xbacklight it doesn't affect the settings in the energy-settings. So my brightness can be at 50%, but the energy-settings say it's at 100%.

Right now I hotfixed it by adjusting brightness via other keys that are recognized by the keyboard-settings. However I would like to use my hardcoded brightness-keys. I think that the XF-keys aren't recognized as such when I press them, but I don't know how to check. Because the xbacklight-commands work fine and the volume-buttons also.

Help would be really appreciated since I run out of ideas. Which doesn't mean much as I'm not that deep into linux architecture..
Thanks.