Brightness on Lenovo not working in Pop!_OS

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On my old laptop, a Lenove IdeaPad identified as Intel Core i7-3632QM processor, Intel Ivybridge Mobile graphics by Pop!_OS, the brightness is not set. Although the Fn key (F11 and F12) are working shown by on screen display with brightness icon, but the is not taking effect. Stuck on whatever brightness level it is.