OK, laptop. That is helpful information. Laptops can have heat issues that desktop computers usually do not suffer from. Dust and debris can clog the relatively small ventilation openings, resulting in heat issues and CPU throttling. Check for that first. Fans can fail also. Try SpeedFan or similar software to check CPU temperatures.

Then, use Task Manager to view the CPU usage, with the highest usage processes set to be on the top of the list. Watch what happens as you perform actions. This might be easier if you can connect an external monitor so you can see the Task Manager window and whatever else you are working on.

If the same process is using the most CPU cycles, you have your answer. If the high CPU usage cycles through various processes, then something else may be going on, possibly with hardware throttling.

Check the S.M.A.R.T. statistics for the hard drive also, in case of retries on read/write operations. Run a memory test as well.

As previously suggested, try a live Linux OS to see if the same thing happens there.

Check for antimalware software using excessive CPU cycles.