Less under center. Less play action. Go more shotgun and let him RPO/straight drop back. Less long developing plays and give him more quick/easy throws. Stop trying to play bully man ball, you don't have the OL or OL coach for it, you can't just arrogantly run with 8 guys in the box. Get your younger play makers more involved at WR/TE. RB there isn't anyone elite there, that includes Wisner, imo.
Right now, it looks more like Manning is overthinking everything and Sark isn't really helping him out. He looks like he wants to call an offense that isn't working and instead of setting his QB up for success might have set him up for failure.
While the OL isn't perfect he has time to throw, he just overthinks what he's seeing. He's also not throwing/playing like he did last yea, not sure if that's because he knew it wasn't only temporary or what.
I should mention you have to do a better job of getting him going early and often. Not run on 1st down, run on 2nd down, okay 3rd and long, oh he missed. Might also need to have some other plays in the back pocket for some red zone plays.
Just my uneducated take. To me it seems like he completely changed what his offense was originally but that's just what I think. Not sure I'd pay for my opinion or coaching advice but just what I'm seeing out there.