I’m also facing similar situation after latest stable update. Tried every solution posted on different forums also but none worked.
Some common solutions are given in this post Can't adjust screen brightness (Lenovo Laptop, NVIDIA, XFCE) but it didn’t work.
After setting kernel param acpi_backlight=vendor, this path is accessible /sys/class/backlight/ideapad/brightness
Anyone having solutions to fix the problem with brightness control?
Is it a kernel issue or driver problem?
Thanks!