I'm not sure that Benfica wants to keep Enzo Fernandez, Benfica just wants to sell the prices of its players for a very high transfer fee. Likewise with another young player, Goncalo Ramos. Benfica is no doubt like the club from the German League, namely Dortmund, they want to sell their young players for a very high transfer value. that is why until now, negotiations for Enzo have been very tough even though the midfielder has actually been willing to play with Chelsea.
in fact, the journalist Fabrizio Romano has stated on his social media. that there is no agreement for the sale of Enzo Fernandez to Chelsea, but there is still time for Chelsea to finalize this deal. however the longer it drags on, the more likely it is that another club steps in and hijacks the deal.
I'm sure, if Chelsea bring Enzo to Stamford Bridge, he can become a mainstay player in midfield to help Chelsea's front line. even so, if Benfica continues to insist on an unreasonable transfer fee. I think it's better for Chelsea to look for other players who have the same qualities as him.