macOS installations shows less space than I have

Question

I cleared my system to install the BigSur beta:

So I have 62 GB free space.

But when Im in the installation process its shows the following:

Just 28 GB free space. How can I fix this?

when I look up my HDD via finder it shows me:

So that 34 GB should be purgable. But how to delete this stuff since my recycling bin is empty.

Answer 1

I found a solution: I just created a new APFS parition and reserved as much space as possible. Then the space which was shown as purgeable was deleted automatically. After that i removed the partition again and had all the free space.

Answer 2

I think there is a problem with your startup drives... Just boot into Recovery Mode and run First Aid.

NOTE: First Aid will temporarily lock the startup volume.

Answer 3

Time machine local snapshots have been known to take up lots of purgeable disk space. Try entering this in Terminal.app

tmutil listlocalsnapshots /

if you see a list of things printed, those are likely using up your space. They are programmed to remove themsleves as your space fills up. Here is a thread with more info on this topic.

If you just want to remove them, you can run this command

for d in $(tmutil listlocalsnapshotdates | grep "-"); do sudo tmutil deletelocalsnapshots $d; done

and then after a few seconds go over to Disk Utility.