Battery and MacOS

i've got updated my mac so far. My mac is "Macbook Air 2017" and currently it runs MacOs Big Sur version. I want to ask that if it's good or not. I can feel that the downloaded apps are running slower than before. Besides, the maximum battery capacity is around 4hrs and a half, which is so disappointing as it's under my expectation although the cycle count is reported to be 415 times.

I'm here to get some advices from Macbook experts and people who've overcome the same situations to expand the battery life.

p/s: am i wrong or not updating my mac?