Next lets try disabling that dell_backlight interface... Please boot with the kernel boot parameter "dell_laptop.backlight=0", verify that only intel_backlight appears when you check "ls /sys/class/backlight", and then test the idle-timeout, lid-close, and brightness keys behavior again. Does disabling dell_backlight help?
@Bobik-s-
Thanks for the detailed explanation.
Next lets try disabling that dell_backlight interface... Please boot with the kernel boot parameter "dell_laptop. backlight= 0", verify that only intel_backlight appears when you check "ls /sys/class/ backlight" , and then test the idle-timeout, lid-close, and brightness keys behavior again. Does disabling dell_backlight help?