Help! My Macbook Pro is so slow, and has always been. After updating Big Sur

Well, you have a lot going on by the look of the report. Sounds like you have some sort of Malware installed on your computer and you need to get that taken care of. That is probably what is using up a lot of your CPU and keeping your computer running slow. You should get some Malware detection and removal software and get that removed from the computer. That should be a large help to get your computer running better.

The update is going to use more resources than what you had before. That is why updates cause older computers to not be able to take the updates because their hardware isn't powerful enough to handle the update. That being said, you could have had things already causing your computer to be overworked, but you didn't notice it because you had an older version of macOS that may not have been demanding as much out of the computer. Still looks like you have some malware that you are going to want to get rid of.