If your Mac starts up to a circle with a line through it - Apple Support

A circle with a line through it means that your startup disk contains a Mac operating system, but it's not a macOS that your Mac can use. 

Flashing Circle with line through it and apple logo when booting

Stuck on circle line logo after disabled unsupported gpu. : r

Crossed out circle at boot up. Recovery n… - Apple Community

Have your Mac speak text that's on the screen – Apple Support (UK)

How to Fix Mac Boot to a Circle with a Line Through it?

Horizontal lines Macbook Pro - Apple Community

Get started with your Mac - Apple Support

Use Siri on Mac – Apple Support (UK)

Mac Boots to Circle with Line Through It 🚫 & How to Fix It

My iMac boots to a circle with a slash in… - Apple Community

Delete files and folders on Mac - Apple Support (CA)

Customize your Mac with System Settings - Apple Support

Startup issue. PLEASE HELP - Apple Community