If the CPU usage is around 100%, this means that your computer is trying to do more work than it has the capacity for. This is usually OK, but it means that programs may slow down a little. Computers tend to use close to 100% of the CPU when they are doing computationally-intensive things like running games.
They are supposed to do that by design - both Core i and Ryzen do this, albeit in somewhat different manners.
You likely have problems elsewhere for the lag, stuttering, etc.
I see in your older threads that you changed motherboards. That alone can warrant a Windows reinstall.
RTX 3070Ti paired with the Seasonic S12III... that is a bad combo. Probably shouldn't be used on anything higher than a GTX 1660 - heck, that model wasn't even made by Seasonic; they outsourced it from another called RSY.
I hope you didn't spend all your allocated budget on the gpu...