Preparing to sell MacBook Pro, HD still shows data on disk

Thanks but that page of information was where I started, which led to my question regarding 200mb of data still showing even after erasing the disk. Since then, I erased everything I could find, then had to reinstall Big Sur. Once that was done, I setup it up again just to see if there was still data use. There wasn’t anything showing in applications, but in Disk Utility it still showed data as being used.

So, once again I deleted everything and restarted in recovery mode. Now when it starts up, I am prompted to reinstall High Sierra (not Big Sur). With that the only available option, I am reinstalling High Sierra, then hopefully can update to Big Sur.

We will see if I have to create a user just to update or not. I really don’t want to do that since I plan on selling the MacBook. Round and round we go!

Good advise, that’s what I would have done except that I had to see if the “200 GB” of data was truly gone. You have to be sure these days with ID theft so prevalent. So I setup up a dummy account thinking I could just reinstall Big Sur and then shut down without setting it up.

Now I’ve done something in error as the only thing that appears is requiring me to choose my network, then Disk Utility shows up and the only options are to restore from a backup or install a new macOS. Choosing to install the new macOS, High Sierra is the only choice and then going forward, the process quits stating that there was an error.

I’m now in a loop and don’t know where to go from here.

OK, so back to Recovery then Disk Utility. I think I’ve gone from bad to worse. Top left under Internal is AppleAPFSMedia and below that is APPLE SSD AP0512J Media. Then under Disk Images is Apple disk image Media and below that is OS X Base System.

I erased the top left item but nothing has changed. When restarting normally, it still comes up to what I already listed, choose network, then options to restore or install a new macOS.

There is an addition issue I haven’t mentioned. Somewhere during the process I was prompted to enter a password to lock down the firmware and since I couldn’t do anything else, I entered a password. Now when the MacBook is restarted, the first thing I see is a lock symbol and a field to enter the password.

I think I have truly screwed up. I long for the days when I simply inserted a DVD and the Notebook would startup reading the DVD and I could reinstall. So simple!

In the end, I called Apple Support. What they had me do different is to not install a new macOS, but instead go to Disk Utilities and from there install the latest OS. I then connected to my home network and Big Sur installed from Apple’s servers. Problem finally solved.

I appreciate the responses from the community, it’s nice to know others are willing to offer suggestions.