After I've erased my MAC, what will appear on the screen when I turn the Mac on?

After you've erased the Mac, if you simply restart the computer you will be greeted with a flashing folder with a question mark inside. That indicates that the Mac cannot find a startup drive with a valid macOS on it. You'll need now to reinstall macOS on the freshly erased drive.

If your Mac doesn't start up all the way - Apple Support

Reboot your Mac into recovery mode and reinstall the OS.

How to reinstall macOS - Apple Support

TIP - After you've erased the startup drive, don't exit out of recovery mode or restart your Mac just yet. Simply quit the Disk Utility app and immediately launch the Reinstall macOS app from the macOS Utilities screen.

JohnS6065 wrote:

After I've erased my MAC, what will appear on the screen when I turn the Mac on?

What is the end game you are looking for here (?)

What to do before you sell, give away, or trade in your Mac

Yes when you Erase the disk it erases everything on the disk.

What do you think Erasing means.

You can't expect to erase your mac but keep all the data on it.

Why do you want to erase your mac anyway.

JohnS6065 wrote:

I'm trading in my MAC and want to make sure all my personal data has been removed

Not a problem—What to do before you sell, give away, or trade in your Mac