Big Sur on M1 was fine ( if not great ), mostly because M1 is extremely fast. But Big Sir on x86 was slow, really slow. I am in the group that reported Big Sur was slower than Catalina, and Catalina was slower than Mojave. That is with both the OS itself and Safari. So Big Sur was not a smooth experience for me.
Monterey so far brings back the speed / snappiness of Mojave. Safari feels so much more responsive under normal use and under heavy tab usage. Lots micro-pause ( Jank ) and lag are gone. As if they put back all the optimisation for x86 previously left out.
Far less Kernel_Task CPU usage and stupid disk write for whatever reason. My guess this is mostly a Safari problem given they have implemented Tab Groups they have at least taken into account of heavy tab usage in mind. This is also apparent when they fix the long standing Tab Overview bug, where it will load ( and reload ) every single Tabs you have trying to generate thumbnail. Imagine you accidentally press the Tab Overview button in the tool bar, or three finger swap in Safari when you have hundreds of tabs. You will instantly get a few hundreds GB of Disk Write paging trying load everything. It is literally a feature that kills your SSD. I have reported this bug for over three years, it is finally fixed. Cloudd and Bookmark / History / Tab Sync pause / Jank is still not fix though. That is 3 years+ and counting.
Still wish they do a list of tabs like Chrome instead of Thumbnails when it is over certain Tabs Number. It is easier to track when you have lots of Tabs. Easier to do Manual Garbage Collection of Tabs.
Bug that causes IINA to crash when viewing video in portrait mode is gone. One of the biggest complain when updating to Big Sur.
WindowsServer also uses far less CPU. It used to hover over 30% for no apparent reason. Now it is back to a normal 5-15% in most cases.
Safari "classic" tabs are back. Along with a very long list of webkit improvement. Far from perfect but at least things are moving.
I am also feeling Apps that are using Swift and SwiftUI are snappier than before and uses less memory. An observation mostly from using Stocks App.
Many other minor details, may be worth reading Ars' review [1]. It is solid release, which along with M1 MacBook Pro sadly dampens my motivation to move away from Apple.
[1] https://arstechnica.com/gadgets/2021/10/macos-12-monterey-th...