solved support.apple.com/mac/startup | mac black screen after | cmd r not working

solved macOS black screen after upgrade on big sur | cmd r not working If your MacBook 20xx starts up to a circle with a line through it A circle with a line through it means that your startup disk contains a Mac operating system, but it¬ a macOS that your Mac can use.  A prohibitory symbol, which looks like a circle with a line or slash through it, means that your startup disk contains a Mac operating system, but it¬ a version or build of macOS that your Mac can use.  follow this step to fix your problem: 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 press and hold: shift+ Cmd+option+R to start up from macOS Recovery.  2- ARM M1 User : after power off, start your mac and hold power key to get into recovery mode 3-While in macOS Recovery, .use Disk Utility to repair your startup disk 4-If Disk Utility didn&find any errors or has repaired all errors or reinstall an os. 5-If you still need help, please contact apple