MacOS not showing up on disk utility

Hi Leslee228,

I'm assuming you have an Intel-based Mac given the device description in the post footer.

You'll likely need to completely erase your Mac and reinstall macOS. If you don't want to completely erase your Mac, let me know and I'll provide steps to see whether we can avoid that.

If you're fine with completely erasing your Mac, complete these steps to fully erase your Mac using Recovery Assistant.

1. Make sure that you have a strong and fast Internet connection.
2. If you previously signed in with your Apple ID, make sure that you have its password ready. You might need to it to clear Activation Lock.
3. Restart your Mac while holding down Command-R. Release the keys when the Apple logo and a progress bar appear.
4. If you're asked to authenticate as an admin, skip to step 7.
5. The Recovery app or the macOS Utilities window should appear. In the top menu bar, select Utilities -> Terminal.
6. Type "resetpassword" without the quotes and hit Enter (Return).
7. The Recovery Assistant app should appear. In the top menu bar, select Recovery Assistant -> Erase Mac.
8. Complete the steps onscreen to completely erase your Mac.
9. Your Mac should restart into Internet Recovery. Connect to a Wi-Fi network if prompted, and then clear Activation lock if required.
10. When the Recovery app or the macOS Utilities window appears again, select Install macOS and follow the onscreen instructions.

Make sure to erase the whole physical SSD which is the item you have selected in the picture. Of course you will need to do this from a macOS installer. I'm not sure the method to "erase disk" within the Apple instructions in the article @Barney-15E linked will be sufficient...it may be, but with an Intel Mac erasing the whole physical SSD is best as it will recreate the whole partition table.

If for some reason even erasing the whole physical SSD still does not give you 250GB (or close to it), then you will have to resort to the command line to destroy the partition table so that Disk Utility will properly erase the SSD. There have been some cases where I've seen Disk Utility get confused if something unexpected occurs with the partition table (usually associated with USB sticks though). I can provide instructions if necessary if the standard erase won't work even after selecting the physical SSD (Apple SSD AP0256 Media).

You will likely need to erase Apple SSD and reinstall macOS, then reinstall BOOTCAMP.

How to reinstall macOS - Apple Support