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A slow Mac is rarely slow for one dramatic reason. It is usually a small pile of ordinary things: a disk that is nearly full, a browser with too many tabs, a background app that has been indexing since Tuesday. The good news is that most of these are fixable in an afternoon.
Start with the disk, not the RAM
macOS needs free space for swap files, snapshots, and updates. When a disk passes about 90% full, the whole system can start to feel sticky. Open System Settings → General → Storage and look at the largest categories before you delete anything.
- Empty the Trash, including old large files you forgot were there.
- Check Downloads for installers and disk images you no longer need.
- Review iOS device backups and old Messages attachments.
- Move finished projects to an external drive or archive.
Then look at login items
Open System Settings → General → Login Items. Every item that launches at startup takes a slice of memory and attention. Disable the ones you do not recognise, then restart once to see the difference. This is often the fastest visible win.
The goal is not a perfectly empty disk. It is enough room for the system to do its job.
Finally, check what is actually working
Activity Monitor shows the truth. Sort by CPU and look for an app that stays above 100% while idle. Sort by Memory and look for a browser tab or a runaway helper. If something is consistently busy for no reason, quit it and see whether the Mac recovers.