Can't update Xcode even with 19gb free space [duplicate]

I have an available update for Xcode that is in the 7gb range, and when I try to update I get an alert saying there isn't enough disk space - I checked my space and I have 19gb available (of 120gb).

Is this correct, or some kind of error? It seems like I have more than enough space.

Update: I deleted some earlier device support files and I now have 24gb free space and I still don't have enough space for the update. I feel like something's amiss here, as the update is only 7gb - I'm not sure if I should keep deleting things to free up space - will it even make a difference?

Update 2: I restarted my computer with 24gb free space and when I clicked Update, the update seemed to go forth and download - however when the download completed, the button switched back to "Update". When I clicked on it again, I got the "not enough space" alert again - even though now I have 26.5gb free space. I restarted again and keep getting the same message. Truly don't know what's going on here! Here's a screenshot, as requested, of my storage window:

Update 3:

Screenshot after running df -h in terminal as per request:

You might be close, but I downloaded from the developer website and I had freed ~22 GB.

Try freeing up some more, like cache or movies you have watched, or software you don't use.

• How can I figure out what's slowly eating my HD space?

• Reduce size of the Xcode application

• Gigabytes of disk space shown as hidden space in DaisyDisk