Not enough storage to update MAC

If the computer has the tiny 128 GB Internal Drive - it is going to a very difficult effort to trim it down to meet the Empty Space Requirements to upGrade to Monterey.

Empty Space Requirements  >> If upgrading from macOS Sierra or later, your Mac needs 26GB of available storage to upgrade. If upgrading from an earlier release, your Mac needs up to 44GB of available storage. 

Empty Space afterwards - it is suggested to keep at least 15% of the Drive Total Capacity as Empty Space for good operations of the computer and for additional updates to Monterey to download, expand and install.

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

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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.

See:

System data is taking half my drive stora… - Apple Community