when can i define fixed size buffer with custom unsafe struct

[sgf]

i saw some information for C# 9.0 at before.
now the .net 5.0 is released!
but we can use it in code ?

public fixed DXGI_RGB GammaCurve[1025];  

[FixedBuffer(typeof(DXGI_RGB), 1024)]    
public ConsoleApp1.<Buffer>e__FixedBuffer_1024<DXGI_RGB> GammaCurve;    
    
// Pack = 0 is the default packing and should result in indexable layout.    
[CompilerGenerated, UnsafeValueType, StructLayout(LayoutKind.Sequential, Pack = 0)]    
struct <Buffer>e__FixedBuffer_1024<T>    
{    
 private T _e0;    
 private T _e1;    
 // _e2 ... _e1023    
 private T _e1024;    
 public ref T this[int index] => ref (uint)index <= 1024u ?    
 ref RefAdd<T>(ref _e0, index):    
 throw new IndexOutOfRange();    
} 

[HaloFour]

Fixed-sized buffers have not been implemented yet. They are still on the backlog.

[sgf]

how can i help to push the process ?
its very helpful for unsafe programming.