I was not surprised by Manchester United's performance. I have seen such a strange performance arm of Manchester United in the last 2/3 years. This is nothing new for Manchester United.
It was Porto's home match. I didn't think Manchester United would win at Porto's home. Even then, Manchester United got a very quick lead in the goals of Rashford and Hojlund. But because of bad defense, they fell behind very quickly. The match was tied at 2-2 in the first half. And just 5 minutes into the second half, Manchester United conceded another goal and fell behind. If Manchester United's defenders performed well, the team could have won the match.
Overall, this match was actually dominated by Manchester United, because it was proven that in this match Manchester United had many opportunities, it was recorded that in this match Manchester United was able to fire 28 shots and 8 shots went straight towards Porto's goal. Meanwhile, Porto was only able to fire 14 shots and 7 of them aimed straight at Manchester United's goal. Apart from that, Manchester United also dominated possession of the ball in this match. However, unfortunately Manchester United could not take full advantage of all these opportunities, so Manchester United was only able to score 3 goals in that match. Apart from that, I also agree with your opinion that Manchester United's defense could be said to be quite bad in this match. The reason is that in that match, even though Manchester United was ahead in terms of score, Porto was able to equalize. Maybe if, for example, Porto's attack line could be a little sharper, I'm sure Manchester United would lose this match. But fortunately Porto's attack line was not too sharp, so Porto couldn't score the winning goal in this match.
And apart from that, I personally quite regret that in this match Bruno Fernandes received another red card. This will of course make Manchester United's midfield even weaker. So in the next match, I am sure Manchester United's performance will be even worse. Because playing without good midfield players, of course it will be a little difficult to get many opportunities. That's why I think that in the next match Manchester United will definitely have an even worse performance. Maybe this season could be a worse season than last season for Manchester United. Because even though this season Manchester United brought in several new players, this did not have a good impact on Manchester United's performance. In fact, you could say that Manchester United's performance is getting worse this season.