Btw, don't think Joan Garcia signs only to be loaned to other club. That's like receiving bad signals from Barca if your future club doesn't think you're good enough to compete for a starting position at the moment.
I think you are overrating Garcia options here. There is zero big clubs that is offering him a starting spot right away.
His only other concrete offer is for Arsenal as 2nd GK for Raya, who is similar but much better version of Joan himself.
Other than that, he is a "maybe" for other clubs. Real is thinking about him as a replacement for Lunin.
His agent is playing games and getting exposed at it, leaking that he has deal with Newcastle, just for their media to confirm they want James Trafford, then it is City, just for their media to say they are after Costa, and before them it was Villa and their media said they are after Chevalier.
Mamardashvili who is a better, more proven GK, who was younger at the time, accepted such a deal, without even guarantees for the future.
Barca should be, absolutely, the one dictating the terms of the deal. Garcia has no leverage, we are his biggest chance for big move.