Check how much storage space is left

macOS runs noticeably slower once free disk space drops below 10–15%. The system relies on that space for temporary files and memory swapping. To check: Apple menu → "About This Mac" → "Storage".

If space is low, free some up: remove unused apps, clear the Downloads folder, and check how much space your Photos library is using — it's often the single biggest consumer of storage.

Too many apps launching at startup

Over time, apps accumulate that launch automatically when the Mac starts and keep running in the background even when you don't need them. Check and disable the unnecessary ones: System Settings → General → Login Items.

Old versions of cloud storage apps, messaging apps and software updaters that you've stopped using are frequent culprits.

When the cause is more serious

If the MacBook isn't just slow but also runs hot, with the fan at full speed even while idle, and the battery drains very quickly, this can point to a cooling system clogged with dust (relevant for fan-equipped models) or a physically ageing battery.

In that case it's worth having a technician take a look — cleaning a MacBook yourself is trickier than a typical Windows laptop because of how the case is assembled.