It is highly irritating that your Mac suddenly becomes to think that it requires a cup of coffee before it can even operate. You certainly do not have to go through the ordeal of having to re-install it all just to regain that speed. It is typically merely too much junk of the culprit attempting to load precisely when you press the power button.
The following is a basic procedure on how to resolve slow boot mac problems and have you back to work (or play) sooner:
1. Reduce What Shows in Your Login pane: System settings General Login items. See that list? These are applications that activate automatically upon start up. Click on those things you do not require at the moment and press the minus (-) button. This is usually the #1 fix!
2. Clean Up the Desktop: You really think that the macOS considers each and every icon as its own window to render on the desktop? In case your desktop is cluttered with files, delete them into one folder. It's a huge relief for your RAM.
3. Check Your Disk Space: Mac requires space to boot up. When you are about to fill your hard drive, attempt to remove some of your large downloads or clear your trash. Aim for at least 10-15% free space.
4. Clear the NVRAM/PRAM (In Intel Mac): Power down your Mac, and then restart it and press at once Option + Command + P + R about 20 seconds. This is a reset of small systems that could be causing the lag. (This is automatically done during a restart in case you have an M1/M2/M3 Mac!).
5. First Aid Check: Open Disk utility (find in Spotlight) and then choose your hard drive and then choose First Aid. It will search through any small errors with directories and mend them to you.
And those should be as fast as lightning on your next boot-up!
