This is absolutely mind-blowing and a very profitable deal for PSG if all parties can come to an agreement. Since PSG already have plans of selling Neymar I feel this is the best offer and opportunity on the table that they can make huge profit from without regrets and can also build up by getting a good replacement and few other additions with this money. With Enrique, things might change as he is already acquainted with the player and will love to be reunited with him again so I’m guessing Neymar’s move will depend on Enrique’s final decision now.
Just because they are offering Neymar a salary of 600 Million € for 3 years does not automatically mean, that PSG will also get a huge transfer fee for him. So no one can really say if this is a great opportunity for Paris to sell Neymar for a huge amount of money. The market value of Neymar is at 60 Million € at the moment and he still has 2 years worth of contract. So i think no reasonable club would be willing to pay more than those 60 Million € for him.
That being said, that Saudi League is just a circus with no sporting value at all. So they probably don't care if they would need to pay 100 M€ for Neymar. Back in 2017 PSG paid 222 Million € for him though, so i don't really think that this would be a very profitable deal for them. They have burnt a lot of money in the last years and have not won the Champions League a single time.