Here is something I wrote yesterday as well...
He is being used outside of his strengths at Barcelona, which can be explained by the presence of Busquets. He is mainly being used higher up the field, therefore not being heavily involved/the go to guy in build up of the play from the back. Where he plays now at Barca you would expect another type of player who is more involved in the final part of the attack and brings goals/assists. He is just not that type of player, never been. He gets criticized a fair share in The Netherlands by certain people that he lacks goals and assists. For me personally thats a load of crap. It would be the same as if we would expect Pirlo/Jorginho/Verrati types of players to provide threat in the opponents box in stead of judging them on their playmaking capabilites from behind the ball.
That being said I honestly think he should leave Barcelona. Barcelona will want to build their new team around Pedri/Gavi/Nico in midfield (which makes sense to me) and Busquets is also still there. Adding Frenkie de Jong to that mix doesnt make a good midfield, because it will mean more of the same players which will eventually result in (as you have seem happening now) one of more of those playing outside position and being used outside of their strenghts. Koeman has used him everywhere in the last year. Wide on the left, wide on the right, as central defender and as #10, but hardly as playmaking #6, because Busquets is always there...