Thanks, Arash.
It is full frame as I stated. The active focus square was on the beak, top row very right square. I did not use noise reduction at all. (Mark IV at ISO 400!!!)
Resized for presentation using "Bicubic sharper". It cannot be any better than that. I mean it is FULL FRAME, Arash.

I forgot to mention what you might see here.
Some bird pictures look OOF because the way the feathers are evolved to blend in.
One exemple is the Long-eared Owl.
Maybe this is what you see here, Arash.
Have you got any American Bittern or Long-eared Owl images?
You can check their feather details. They might look the same on your pictures.