Why does my computer work better in Safe Mode?

Safe Mode uses a limited set of Microsoft drivers and services, so the performance improvement strongly suggests something loaded only during a normal start. Perform a clean boot using Microsoft’s procedure, then compare performance. If the clean boot is fast, re-enable disabled services in halves and restart after each change until the slowdown returns; repeat with Task Manager > Startup apps. Keep security and Microsoft services enabled while testing. In Task Manager, sort Processes by CPU, Disk, Memory, and GPU during a slowdown and record the consumer. Update chipset, storage, graphics, audio, and network drivers from the PC manufacturer, or roll back the driver whose installation matches the first occurrence. Run a Microsoft Defender scan and verify adequate free disk space. If a clean boot remains slow, test a new Windows profile and run DISM /Online /Cleanup-Image /RestoreHealth followed by sfc /scannow. Avoid registry cleaners because they obscure the comparison.