How to Format/Clean my iMac so I can start fresh with just my essentials?

[igilphoto]

I'm sorry if this is asked a lot, I just usually see people do it before selling and I have a bit different case so wanted to hear your opinions.

I have an 2019 iMac, I'm a photographer and bought it for work in the middle of the wedding season last year so. I used "Time Machine" to migrate from and older mac with older files and programs, and also during the last year of daily use it collected a lot of junk on the HD.

Maybe I'm just paranoid and bored after all this quarantine, but I feel like the mac running a bit slower than it used to. And I also have a feeling that there's too much junk so I prefer to start clean. I don't have any ongoing projects on it so seems like the right time.

What is the best way to do it? I already backed up everything.
Just format everything back to factory settings and install what I need? How to do it? Or is it unnecessary ...

Preferably I would like to keep things like internet data and some preferences/programs on the mac itself but its not critical

The most important thing to me is that I want to make sure that my mac is clean and secure, any tips will be appreciated .
Thank you

 

[Fishrrman]

1. Boot to INTERNET recovery (NOT "the recovery partition):
Command-OPTION-R at boot.

2. Open disk utility and choose "show all devices" from the view menu (VERY important step)

3. Locate "top line" on left in disk utility that represents the internal drive.
ERASE it.
If you're using Mojave or Catalina, erase to APFS with GUID partition format.
Anything else, I recommend Mac OS extended with journaling enabled, GUID partition format.

4. Once erased, open the OS installer and do the install. The computer may restart one or more times, screen may go black for a few minutes, you then may see several progress bars. Be patient.

5. Once the install is done, begin setup ("choose your language"). At the appropriate moment, setup assistant will ask if you wish to migrate from another drive. If you want to do this, connect the backup drive and give setup assistant time to "digest everything". Be patient.

6. Setup assistant will present you with a list of stuff that can be migrated. You can either accept the defaults or customize it. Up to you.

7. When setup assistant is done with the migration, you should see your login screen.