I am getting

'A type is missing in a collection expression'

Which is cause by the doc block @var array<string, mixed> such as found at https://github.com/netgen-layouts/layouts-core/blob/7fbe0c1b0619fc8f33dacddeea2ada7af484a4b8/lib/API/Values/Block/BlockUpdateStruct.php#L76.

array<string, mixed> is generated suing phpStan. I believe array<string, mixed> is a valid type.