Not enough disk space for Monterey.

It is possible that the installation process is encountering an error or there may be other factors contributing to the not enough space error. Here are a few things to check:

1. Check that the size of the installer file you are using matches the size of your SSD. It's possible that you may have accidentally downloaded a smaller version of the installer.
2. Verify that your SSD has enough free space to install the operating system. While the size of the installer is around 20GB, the installation process requires additional space for temporary files and other system files. As a general rule of thumb, you should have at least twice the size of the installer available in free space.
3. Ensure that your SSD is formatted correctly for macOS. If the SSD was previously used with a different operating system or formatted in a different file system, it may need to be reformatted to work with macOS.
4. Check that your computer meets the minimum system requirements for the operating system you are trying to install. If your computer doesn't meet the requirements, the installation may fail or encounter errors.