Not booting up

This question has appeared several times a month in ASC.

Simply put, "the Mac cannot find a system, or the system is

lost or damaged."

Sometimes a symptom makes for quite a detour to resolve this.

Here's a situation where you'd not tell what goes on, by title:

• Q: I am about to sell my 2015 MacBook Air... - Apple Community

https://discussions.apple.com/thread/253278820?answerId=256144896022#256144896022

[While a reply covers more than two possibilities; and cure(s) within one.!]

• Start with this, instead of all that..

• If your Mac starts up to a Question mark - Apple Support

https://support.apple.com/en-us/HT204323

"A folder with a flashing question mark means that your startup disk is

no longer available or doesn't contain a working Mac operating system."

• " If your Mac starts up to a Question mark: "

1. If the question mark appears only momentarily before your Mac starts up normally:Reset NVRAM.
2. Make sure that your preferred startup disk is selected in Startup Disk preferences.

• " If the question mark persists, follow these steps: "

1. Press and hold the power button on your Mac for up to 10 seconds, until your Mac turns off.
2. Turn on your Mac and immediately press and hold Command (⌘) and R to start up from macOS Recovery.
3. While in macOS Recovery, use Disk Utility to repair your startup disk.
4. If Disk Utility found no errors or repaired all errors, reinstall macOS.
5. If you still need help, please contact Apple Support.

Good luck & happy computing!🌻☃️🌿⛵️