How to cancel macOs installation during its installation?

ttthaor wrote:

I upgraded to Monterey but the process couldn't be completed since my mac doesn't have enough free space left. It seems like it's stuck on half way through. When I boot my mac in Recovery mode, it says "Reinstall Monterey" instead of my previously installed system. So I can't choose to reinstall my old macOs system in Recovery mode anymore. Now once I turn my mac on it jumps into the login screen, and after entering my password as usual, it will comeback to the macOs installing screen (with black screen and Apple logo, stuck-at-the-middle loading bar and "estimating time left"). How can I stop it from jumping into Monterey installation so I can make a bootable installation with another operating system that my mac can handle? How do I quit this loop?

You can try a SafeBoot when you restart hold the Shift key.

 How to use safe mode on your Mac - Apple Support

If neccessary you can always force quit a shutdown by holding the power button/TouchID for ~6-10 sec.

Force Shut down your Mac.

Log out, sleep, wake, restart or shut down your Mac

Shut down or restart your Mac - Apple Support

Follow the advise from previous posting first.

Fall Back positions if needed

1 - Transfer files between two Mac computers using target disk mode - Apple Support (CA) and hope you can move enough of your personal files Off the problematic and Stuck Computer

2 - Last Resort of all

Scorched Earth Method 

This method will WIPE ALL Data and there is No Recovery - Period.

To perform this action will require booting from a Bootable Installer. 

The Bootable Installer can Only be performed on an Apple Computer 

This will have to be performed from a Qualifying Computer to run the version of macOS to be made on the Bootable Installer.

Only an Example : Bootable Installer of Big Sur would have to be done on a computer that Qualifies to run Big Sur.

Notation: If the computer being used to perform this action is Too New or Too Old to qualify to run the version of macOS - this computer can not be used.

Alternative is, to gain access to a Qualifying Apple Computer from a family member, friend or associate.

Once that is done read on for preparing the Destination computer  >> Only works on Intel Based Apple Computers.

Extra Special Notation regarding the Touch ID equipped Apple Computer.

About Startup Security Utility and Must Enable from Recovery Mode the ability to boot from External Drive Before Attempting 

1 - Shutdown computer and disconnect all external drive Except the newly created Bootable Installer.

2- Restart and immediately hold the OPTION key until the Startup Manager appears and choose the USB Drive. 

3 - It will present options >> Disk Utilities >> View >> View ALL attached Drives. 

4 - Choose the Upper Most Drive ( not the volumes indented and list below ).

5 - The drive normally is called Apple Media or Apple SSD - that is the drive to Erase and format as APFS with the GUID Partition Map. This applies to macOS 10.14 Mojave and above. 

5A - Formatting for macOS 10.13 High Sierra and below requires HFS Journaled with the GUID Partition Map

6 - Once that is done >> backup out of Disk Utilities and choose install macOS. 

7 - Follow the prompts and it may automatically reboot several time. 

8 - Upon a final reboot - Setup Assist will present with the newer version of macOS.