High Disk, CPU, or Memory Usage for No Reason

My Windows 11 PC has been running painfully slow lately, and when I open Task Manager, I see that disk usage is pinned at 100% and memory usage is hovering around 90% even when I have no applications open besides the Task Manager itself. I've already checked for malware, disabled all startup programs, and updated my drivers, but the high resource usage persists constantly, making even basic tasks like opening File Explorer or typing in a document feel sluggish and unresponsive.