Cannot upgrade

you can purchase an external HDD or SSD of sufficient capacity and move your larger files (videos, pictures, documents, etc...) to it. once they are on the EHD, you can simply erase the same files from your internal drive. and, if it's just going to be used for storage, you can use an HDD and save a few bucks over the cost of an SSD. FWIW, i personally keep very little on my internal drive.

also, you may want to read these two articles:

Optimize storage space on your Mac

How to free up storage space on your Mac

Quemfala wrote:

Thank you. Do you know if when I backup my photos to an external hard disk if the date created and location are also copied?

yes.

f I back-up my photos to a HDD, then I would definitely have disk space to upgrade. However, I hesitate to do this because I not sure how I would look at photos once they are no longer on the computer.

with the external drive connected to the mac, you can look in the finder sidebar under "locations", and open it from there.

Are the photos in separate named folders or are they all thrown together 'in one pot'?

that would be totally up to you. however you decide to organize photos into folders, by name, date, etc is what you will see in the end. it also depends on if you move the photos one by one, or entire folders at once. the possibilities are endless. :)

and i would also verify for myself that the photos were successfully copied to the external drive BEFORE deleting them from the internal drive.

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

Locate backups of your iPhone, iPad, and iPod touch

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.

The Other Category as defined by Apple is a area of the Operating System that the User ( you and me ) can not Manage.

Manage as in remove, alter, modify or delete.

Therefore, if this Category is taking up needed space on the computer that is required the upGrade to Monterey , the supplied links in previous posting may offer a way to clean up Personal Files and thusly allowing the upgrade to Monterey.

If the required space is not created by removing enough personal files - the upgrade to Monterey can not happen.

and FWIW, it's recommended to have at least 35 - 40 GB free space to perform the upgrade.

you're welcome.

Quemfala wrote:

I back up important document files onto an external hard drive. Is this the HDD you are referring to?

yes, i am referring to a hard drive (HDD), or a solid state drive (SSD). SSDs are much faster, but also more expensive whereas HDDs are slower but also less expensive. when i go shopping for an external drive, i choose HDDs for storage, but i also have 2 SSDs that i use to each run an alternative macOS.