Arsenal lose so many players: Zinchenko, Saka, Odegaard, Merino, Calafiori, and Tomiyasu, if Arsenal will play without them, I doubt they will able to beat Atalanta. These players are very important for Arsenal especially Saka, without him, Arsenal is rarely to score a goal.
As for Liverpool vs Milan, both of them have a chance, anything can happen. However I expect both of them won't score many goals.
Saka and Calafiori are questionable, so there is a chance that they will be able to recover for the match with Atalanta. And Arsenal plays much more consistently, their game is not as good but still it is better than the ups and downs that Atalanta has, like losing 4-0 to Inter. These teams are focused on attacking football, so you can expect a lot of goals, but I remember how Arsenal played in the Champions League, it seemed like it was a completely different team, Arsenal in the Premier League in the Champions League stood out for its scoring.
Arsenal is in a better position against Atalanta. Atalanta's important striker Scamacca is injured for a long time. Therefore, he will not be able to play in any Champions League matches. Arsenal can take advantage by taking advantage of the opportunities they have. There may be compensation in the Premier League, but it will be very difficult to compensate in the Champions League. I expect Arsenal to win this match.