Note: I can not replicate it, welcome any guidance to replicate it

Settings/System/Storage/Storage Spaces, on Windows 11 (Home OR Pro), the wizard maybe fail if you do things in certain order, and the reason is, its volume requirement is complex and unknown.

CannotPoolReason: Insufficient Capacity

Step-by-Step

1. Add a pool using a large physical disk. 3GB does not work, but 15 GB works. A .vhdx (Dynamically Expanding) can help you allocate 1500GB with 100MB real cost. Skip New Storage Space/(Add a space).
2. Physical Disks, add a disk whose volume is lesser than the requirement but it may be pass, idk why but i encounter it, if pass, failure will occur. I use 100MB.
3. Physical Disks\(large volume)\Properties\(Try to remove it), The Trap: The GUI do not tell you that the small disk has no capacity.
4. Add a space. Well, An error occurs, and you can not add a space, all Physical Disks disappear under the pool.

Behavior

Check all disks via PowerShell:

Get-PhysicalDisk | Select-Object FriendlyName, CanPool, CannotPoolReason

For .vhdx, it is

Msft Virtual Disk False Insufficient Capacity

, where Insufficient Capacity just means it is too small.