More specifically the game-day head coaching game management decisions, which to be fair McDermott has gotten better at but yesterday's effort was poor.
Game Management involves making decisions which help maximize your team's chance of winning. For instance the failed 4th down at midfield was one where the risk far outweighed the reward even if it had succeeded. It seemed to be a nod toward the trend of "go for it YEAH i got cojones!!!@" lately in the league; that pendulum may have overswung.
The timeout on 4th and 17 speaks to "I don't trust my game week coaching without micromanaging this down." This wasn't an obvious fustercluck like those 1st half TO's were. The play that was aborted by the timeout, Mahomes was under instant pressure because his line was gassed and discombobulated and he had to chuck n' duck, that play was DOA. But thanks to the timeout they get into a much better play, the Bills inexplicably put on a eunuch pass rush on the down and they convert.
The FG attempt as well, a punt even through the end zone leaves them at best < :20 and a 20-ball needing a TD. That's a whole lot less threatening than the Chiefs 42. There has to be charts, stats, analytics showing this stuff. You don't need to be a legendary HOF gameday coach but jeez, just be average or get someone who understands this stuff into your headset.