MacBook problem

Briefly stated if you upgraded that Mac to Catalina (or later) from some earlier macOS release then its startup disk was reformatted to a file system its originally installed operating system (Sierra, perhaps) does not recognize, hence the blank page. If that's the case the solution is to be sure to select "Show All Devices" from the Disk Utility View menu, choose the topmost device, and erase it.

• "Device" in this context means the hardware with an immutable name such as "APPLE SSD MEDIA..." or words to that effect. That's what needs to be selected, and erased.

You probably ought to start from the beginning and describe how you arrived at the need to reinstall macOS. It might not be necessary, it might not fix whatever underlying problem there may be, etc.

That settles any uncertainty. The startup disk / internal storage has failed, or a related hardware fault exists. As far as the Mac can determine, there is no startup device.

Make an appointment to have that Mac evaluated: Official Apple Support

Apple's evaluation is free and the quoted price will be accurate. It can be fixed, but whether the cost involved is economically justified is for you to determine.

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