disk reported as full in disk utility but not elsewhere

Freeze/crashing often is related to lack of RAM. Not "disk memory" but ... CPU memory.

So if you run activity monitor, you can see how much memory you're using, how much is free, how much "pressure" your memory system is under.

Activity monitor summary looks like this:

and you can look at each application to see if one is a hog. But on a good day, Swap Used should be pretty low, and memory used should not be pushing up against the physical memory amount.

My other app shows me a different view (iStat menus):

It shows me that Safari is using a TON of memory and that sucks. When that happens I usually quit the browser and restart it.

Another sign of not enough memory is "page ins and page outs" which as you can see on my brand new laptop are 0! That's because I have 32G of RAM now instead of 16Gb.

So ... I hope this gives you something to think about. If you want, post how much RAM your computer has, what model Mac you have, and maybe even sort your activity monitor by Memory (in the Memory tab) and see which apps are using the most.

Cheers

Don't worry, your disk isn't full.

You clicked on the top level item and it's displaying the partition map, not a map of how full your hard drive is.

Mine looks the same.

If I click on the Macintosh HD (volumes) item, which is the third one down for me, and I think you, it tells the truth.

If you want to use the Terminal, you can check this way as well:

[Key-Lime-Pie.local:18:22:27::~]

$ df -h .
Filesystem     Size   Used  Avail Capacity iused      ifree %iused  Mounted on
/dev/disk3s5  926Gi  309Gi  601Gi    34% 4370805 6298326280    0%   /System/Volumes/Data
[Key-Lime-Pie.local:18:22:35::~]
$ 

Actually, to be honest, with APFS, there are things I don't even understand. It's a super sophisticated file system.

Also, the last entry/pic seems like the best, the one with Data in its name, not the one which says "Snapshot".