I had the same issue, I updated my Macbook Pro from Catalina to Big Sur, and the battery life was terrible and my computer would get boiling hot. I got a message saying that "battery capacity is significantly reduced" and I powered off my computer and start it up while holding "Command + Option + P + R", which reset the PRAM and solve the message but my battery life was still trash, I then check my CPU usage and there was an app called "Google Chrom Helper" which took up 95% of my CPU usage. I force quit it then immediately notice a cooler Mac and faster response times. I would try looking at CPU usage first.