Do grandmasters practice blindfold chess or does it come naturally with practice? Since grandmasters are good at calculation, do they practice blindfold for improving calculations, or does it come naturally over time by solving a lot of  complex calculations?
Your question is quite interesting. If you are new to blindfold, I think this thread will help you: Can playing blindfold chess be learned or is it a natural skill?
Now, back to your query. I have discussed this topic with a GM, who is one year senior at my college. According to him, playing blindfold is &quot;NOT impossible&quot;, but it's fairly difficult. As they participate in lots of classical tournaments where they have to write the scoresheet by hand, it is easy for them to quickly visualize the board. Also, their training process helps them to calculate from certain positions without playing the moves. But, on the other hand, it is fairly difficult to keep up every possible move, visualize every possible position and that needs intense focus and concentration. But, since they are calculating and visualizing chess more often than normal people, it is comparatively easy for them to play blindfold chess after practising for some time.
In a nutshell: it doesn't come naturally over time without practice, even if you are a GM.