If I remember correctly Sassuolo had an agreement with Juve last year to sell him for €18m this summer. If Juve sell this summer, it is because they are looking for a quick profit. I read Milan are interested in him.
The story is most likely BS. Juve had already an option to buy him in January, they organised the purchase with Sassuolo, and Sassuolo would have a percentage on any sale over the next 2 years, so a sale would make sense only for a very high price.
Milan is rumored to have asked for him but so far the only option offered by Juve, IF Sarri decides he will not need him this year, is a loan or a sale with option to buy back. I can never exclude a sale by Juve but given the context it would require a very high price certainly not below 40M since the club will certainly need another CB next year if not this already.
The guy has had a fantastic second half of the season becoming a starter with Sassuolo immediately and had a great game with Turkey. Hi is a physical marker not a passer so he would be the ideal sub for Chielini. He is also very good with his head and can score.
Juve also bought another quite good young CB, Romero who has been left on loan to Genoa.
I think next year the best out of Romero, Demiral and Rugani will stay on long term and the other two will be sold, but I do not think it will happen now