It's a pity for Haaland. Pep's decision to take him off so early is probably to avoid breaking the record. It makes no sense to take off a player who has scored 5 goals on the way to a new record. What Pep did is very wrong and from what I see on social media there is a big lynching.
I didn't expect it to be so easy but I expected City to have a comfortable game at home, I thought they wouldn't push any harder when they had a comfortable score in the first half but it wasn't like that. They kept scoring goals in the second half.
You can't blame Guardiola, he may have a big reason to change Haaland with Alvarez. Guardiola may think about keeping Haaland's fitness, he probably feels worried that Haaland gets injured because playing too aggressively. Man City still have some crucial matches in EPL and they still need Haaland in the next stage/round of UCL. So, keeping Haaland's fitness is more important than chasing the record.
Napoli scored at the end of the first half, it looks like this is the end for Frankfurt. Real Madrid and Liverpool looked equal in the first half, but perhaps the reason is that such an score is quite suitable for Real Madrid.
Napoli played very well, they dominated the match and scored 1 goal in the 1st half. I see no chance for Frankfurt to come back, they are simply eliminated in this round. It is a home match for Napoli, they will continue to play offensively. The aggregate is 3-0 for Napoli, it is enough for Napoli to qualify for the next round.
Real Madrid and Liverpool scored no goals, they played equally in the 1st half. Both played very carefully, so it is difficult to expect many goals in this match. So, it seems hard for Liverpool to score 3 goals in 2nd half and qualify for the next round.