I haven't heard any rumors about this, or maybe Thomas Tuchel?
Is he really the right man for this job though? I think people criticized him due to what he stated in the media about the possibility of him going to Spain recently. Not sure if he's doing it on purpose or not, but judging from his past history I'm struggling to see him as a man to revolutionize a club in the brink of financial troubles and management's silly decisions. If what Xavi's said about his experience is true (whether you believe he's exaggerating it to reduce the blame on himself or not), I don't think Tuchel is going to last longer than 2 seasons at most.
Tuchel is not a fan of sexy football and he is not a coach who can match with Barcelona's tradition. Barcelona are favorite to choose coaches from Spain or Netherlands because their success last two decades comes from foundation of a Dutch man, Johan Cruyff. After Cruyff, there are some coaches from Netherlands work for Barcelona like Frank Rijkaard, Ronaldo Koeman. After success with Pep Guardiola, they succeeded with another Spanish coach Enrique who is working for PSG in this season.
If Barcelona want to hire a German coach, they can consider Klopp but will have to wait one more season because Klopp announced that he will take 1-year off after this season. He can aim at a coach position of Germany national team because the contract of Nagelsman lasts only till the end of Euro 2024.