The Simmons - Embiid lineups just don't work with Brown coaching.
I suspect it's more the two players and not the coach, but that's me.
I'd deal Simmons (Embiid's the far better player, though he is injury-prone) for an elite shooter.
Devin Booker for Simmons would be an interesting deal, for example, and would balance the Philly lineup by himself. The defense would take a step back, as would the play-making, but the gravity of Embiid would allow for more open shots from Harris, Booker, and Richardson. Horford could then be played as a PF/ C hybrid in the minutes Embiid's not on the floor (or they could go big when playing Milwaukee and other large teams).
Zach LaVine could be a part of another interesting package. LaVine and Coby White for Simmons and Thybulle?
How about a blockbuster wherein Miami deals Bam Adebayo, Duncan Robinson, and Tyler Herro for Embiid?