I am curious if in Ligue 1/PSG they can offer player options to give the player more insurance and flexibility. In football I hear more often clubs exercising options (United extended a year for Rashford that was their call I think). However I think Alves had one at Barca and gave up a year he could have had to leave.
League rules for no buyout clauses are really short sighted. Let clubs use them if they want. In La Liga, Real effectively doesn't do them--write in buyouts of a billion dollars so it is effectively worthless, but others do like Barca and Atletico.
Release clauses are mandatory in spanish law. It is not a specificity of football.
It doesn't exist in France and is strictly illegal according to the french football rules. A club could theorically risk a sanction if such a clause is discovered.
I read somewhere that the fact they could put that clause on his contract has given the final edge to Juve. Good job from them securing the transfer. Imo, it is not too bad for PSG because if he is adamant to put a clause, it means he doesn't expect to stay long term. PSG always sign that kind of players to keep them.
Still, 150 M is quite high for a defender and i see no one paying that. So he could well do his whole contract there. And Juventus is sending signals they are pushing for CL with those big signings.