can't install monterey

What is “Other” storage on a Mac, and how can I clean it out?

Free up storage space on your Mac

OmniDiskSweeper Safe to use

GrandPerspective 

How to delete Time Machine snapshots on your Mac

See used and available storage space on your Mac

The final word from Apple on Managing the " Other " Category

Other: Contains files that don’t fall into the categories listed here. This category primarily includes files and data used by the system, such as log files, caches, VM files, and other runtime system resources. Also included are temporary files, fonts, app support files, and plug-ins. You can't manage the contents of this category. The contents are managed by macOS, and the category varies in size depending on the current state of your Mac.

You need 26 GB of free space to install Monterey. See the previous link on how to free up space.

Free up storage space on your Mac

The boot drive is the internal drive of the computer. With only 18 GB empty space use any of the suggestions from both Old. Toad or P. Phillips ( me ) to try and remove large files on the internal drive

How much free space do you have on your boot drive?

How big is the boot drive?

Are you trying to install an update or an upgrade? If an upgrade what system are you currently running?