The boat has sailed for Mazaroui. Would have welcomed him last summer on free. We had weathered the storm, and now it's time for the next step. Mazraoui is not that attacking, nor he's a clear upgrade on either AWB and Dalot.
I don't know where you get this impression about French clubs overprice their players and not German clubs. For every Ndombele, Pepe we had Werner, Sancho, Naby Keita from German clubs. Tchouameni, Mbappe, Martial with hindsight looks like pound for pound the correct value. French clubs let Kante, Muani, Coman, Nkunku, Konate, Camavinga, O.Dembele... went to other other leagues cheaply.
You're looking Leverkusen who rinsed Chelsea for Kai Harvetz sale. So the question is all about whether the player is worth the fee. Fringing looks to be more of a wingback than full back. Not sure Fringpong fit the profile we're looking for our RB position.