Have you looked at Task Manager?
If not, here's how (I am talking about Windows 10--don't know if this will work in 11):
1. Press, simultaneously, Control, Alt, Delete;
2. A menu will appear: select Task Manager
3. The first screen is Processes: it will have a number of columns, the first of which is labelled CPU.
4. Look down this column to see if any App or Background Process is taking a lot of CPU.
5. If you see something you don't recognise that's using more than about 10%, Right Click and select End Task.
6. See if things improve. Or alternatively, your computer may stop working, in which case turn off the power and then turn it on again.
Often the cause of these things is Windows downloading huge amounts of updates, which it hasn't told you about; this can kipper performance for a couple of days, in the worst case.