Olaylar= record
1024Bytes = array[0..1023] of byte;
OnRx: procedure(const RxBfr: 1024Bytes; const DataLen: word); stdcall;
OnTx: procedure(const TxBfr: 1024Bytes; const DataLen: word); stdcall;
end;

I think it would be something like:

public struct Olaylar
        {
            public _1024Bytes Bytes;
            public Action<_1024Bytes, uint> OnRx;
            public Action<_1024Bytes, uint> OnTx;

            public struct _1024Bytes
            {
                private byte[] bytes;
                public byte[] Bytes
                {
                    get { return bytes ?? (bytes = new byte[1024]); }
                }
                
                public static explicit operator byte[](_1024Bytes bytes)
                {
                    return bytes.Bytes;
                }
            }
        }