Predicated on user's byline " iMac 24″, macOS 15.1 "
This computer is an Apple Silicon computer that needs an external mouse
What brand of mouse is being used and how it the mouse connected to the computer
Having to Force Quit Applications to get the mouse to function is usually an indicator of Heavy Usage
Use the Activity Monitor application and make sure to use View >> View All Processes
What process or processes are using the Most CPU and Memory.
Often times, the issue maybe a combination of Processes
When the computer is using so much CPU / Memory, it can also be an indicator of a Lack Of Empty Space on the Drive.
In which case, the CPU and Memory usage would become much more because it is searching for Empty Space to save all the Changes the user is performing.
How many Web Browser tabs are in usage.
Each tab may have content that is consuming great amounts of CPU / Memory .