Large amount of storage space I do not know how to delete

Big Sur—Press release states that you will need 35.5 GB of free storage when upgrading from High Sierra or newer, and 44.5 GB when upgrading from an older versions—this allows for the unpacking/rearranging of the Installer itself. After it is complete the system only takes up ~ 14.9 GB APFS Volume ⁨Macintosh HD⁩

See used and available storage space on your Mac

https://support.apple.com/guide/system-information/see-available-storage-space-syspf9b375b9/10.14/mac/10.15

How to free up storage space on your Mac - Apple Support

https://support.apple.com/en-us/HT206996

User tip: "Other and What Can I Do About It ?"

https://discussions.apple.com/docs/DOC-5142

Thin local snapshots :

ref: https://eclecticlight.co/2020/04/09/where-did-all-that-free-space-go-on-my-apfs-disk/

Try something like OmniDiskSweeper for a GUI to get a good look at itemized file size and location:

OmniDiskSweeper http://www.omnigroup.com/more

I probably can't explain where everything is, but the header "Documents" on the left doesn't imply your Documents folder. The File Browser on the right is showing your Home folder contents. Note that your Documents folder (and Desktop) is not listed. That is likely because you have Desktop & Documents in iCloud Drive enabled. All of the documents in your Desktop & Documents folders are not shown in that File Browser folder.

As leroydouglas already posted, use a tool that works. Apple's storage displays are so useless they might as well remove them.

MrHarvey23 wrote:

I see, I was thinking it would display all my documents.

As recommended in some forums I downloaded and purchased a licence for CleanMyMac, and it worked pretty well. I also found I had a lot of GBs in my Xcode folder so wiped them. Still don't have enough space for the Big Sur update though!

Thanks for the help.

Well you do not need the graphic user interface to drill down on an issue, much like your "CleanMyMac." typically these third party cleaners, optimizers, anti-virus cause nothing but added issues.

From the Terminal.app you can  see more detail copy & paste the command line:

sudo du -h -d 1 ~/

File size, and finding missing GB— list the items in the home folder with the sizes, including invisible items.

Further more:

sudo du -h -d 1 /

File size, and finding missing GB —will list the items in root with the sizes, including invisible items.