As you can see, the teams that finish top of Pool A, B, C and D will face a third-place team in the Round of 16, while the teams that finish top of Pool E and F will face teams that finished second in their pool. Likewise, some teams that finished second in their pool may face the winner of another pool, while some will face the runners-up.
While on the surface that may seem slightly unfair, that imbalance is addressed in the next round. Let's take Pool A and Pool E as an example. The team that wins Pool A will face a third-place team in the Round of 16, but in the quarter-finals could potentially meet the winner of Pool B if that team wins their Round of 16 match.
On the other hand, the team that wins Pool E will face a runner-up rather than a third-place team in the Round of 16, but in the quarter-finals would face the winner of a quarter-final between two other runners-up. So while the winner of Pool A would face a third-ranked team and then potentially a top-ranked team in their games, the winner of Pool E would face second-ranked teams in both games. There's therefore no advantage or disadvantage to be gained or lost regardless of your team's raking at the end of the pool stage, it will all even out in the end.