Create Partition for Mac OS Beta

The release notes for Mac OS 11 Beta 11 states that installing the beta in a volume will prevent future updates to other OS versions on that partition. With that in mind, I want to create a new partition, but I'm having problems.
First of all, I tried Disk Utility, but it won't let me change the existing partition.
In the partition screen, the '+' is disabled, and the screen says:
"This container has 236 GB used space.
Its minimum size is 449.96 GB.
This container can't be split, because the resulting containers would be too small."

So I looked into resizing the existing partition. In terminal, I entered:
sudo diskutil apfs resizeContainer disk1 450g

but it failed with the error message:
Aligning shrink delta to 49,963,175,936 bytes and targeting a new physical store size of 449,999,998,976 bytes
Determined the minimum size for the targeted physical store of this APFS Container to be 499,963,174,912 bytes
Error: -69521: Your APFS Container resize request is below the APFS-system-imposed minimal container size (perhaps caused by APFS Snapshot usage by Time Machine)

Does any know why this is failing, and how I can fix it?
I think I solved it. this command:
Code Block
sudo diskutil apfs resizeContainer disk1 400g apfs Extra 100g

resizes a 500 GB partition to a 400 GB partition and creates a new 100 GB partition named 'Extra'.

Adjust the parameters to suit your setup. 100GB seems to be the minimum size, the Xcode.xip won't extract on a 60 GB container complaining about the lack of space.

Now you can run the Install Mac OS Beta, select 'Show All Disks' and the new partition should appear. Install the new beta on that disk.

Create Partition for Mac OS Beta
 
 
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