If you have noticed that your Mac computer is taking longer to start up significantly, and wish to speed up the process, try some of the suggestions outlined below.
Keep the macOS up-to-date
It may be annoying but installing all available macOS updates in due time is a great way to keep your system safe, resolve potential software conflicts and receive performance optimizations. To check if you are running the latest released version, go to the Apple menu, choose 'About this Mac' and press 'Software Update.'
Check the available space on the drive
If your boot drive is running out of space it could cause various issues, one of which is increased startup time. A good threshold to keep in mind is having at least 10% of the total capacity available. If you have passed that limit, consider deleting the cache, junk and old log files. To speed up the process, go to the Apple menu and choose 'About this Mac' again. This time go to 'Storage' and press 'Manage.' Take a look at the displayed recommendation and follow the ones that fit your needs.
Turn off FileVault
If the contents of your startup disk have been encrypted with FileVault, it would increase the time that operations need to read or write to it naturally. Keeping FileVault turned on is generally recommended, but your goal is to speed up the startup of the system then consider turning it off. To do so go to the Apple menu, followed by System Preferences. Select 'Securitiy and Privacy.' Open the 'FileVault' tab. Click on the padlock and enter your admin username and password to unlock it. Now, press 'Turn off FileVault.'
Try an NVRAM reset
If nothing else helps, try doing an NVRAM reset. Start by shutting down your Mac. Then, press the power button and hit and hold Option+Command+P+R on your keyboard immediately. Keep the keys pressed for around 20 seconds. Afterward, release the keys and wait for the Mac to boot normally.