YOUR NEXT STEP
Modern macOS is designed for fast SSDs. Older mechanical hard drives simply cannot read data fast enough anymore, causing the entire system to wait.
A compatible SSD upgrade can improve responsiveness on some older Macs. Check model support, drive condition, backups, and the actual bottleneck first.
A symptom can have more than one cause. These guides help you choose a next step; confirming a hardware fault requires testing.