You buy your ticket, arrive when you want, go for a pint when you want, and leave when you want, it's your own business.
Don't argue though that it doesn't look bad when Haaland is going around the pitch after a hattrick acknowledging the fans, and a huge number have already gone. Or when he's being honoured for breaking the goal scoring record, or we needed a late winner against Everton last year, and huge numbers have left, don't pretend that doesn't feed into the "City Fans are flaky" narrative. The people who stay to the end to "support" the team and the players are just different, but be free to leave whenever you please.
Rather than critise early leavers, I'm more impressed with the numbers that can get to so many games, juggling family, work, weather, transport and cost, so if you need to go early, that's fine, thanks for coming and making the effort. I suspect some critics of early leavers don't go to as many games as those they attack for departing early. The additional playing time this year might make the problem worse, or better, they may realise how much they're missing after minute 80.
Interesting for me that for Madrid at home I was very vocal about the club's ticketing policy excluding true blues, and potentially ruining the athmosphere with tourists, and non-City fans. I was the only one of our group of 5 Match Day buyers to get a RM ticket, sitting on my left was an Asian girl and on my right was a Middle Eastern guy. They were in their seats well before kick off, didn't go early for half-time pints, were in their seats before the start of the second half, and stayed well after the finish, they joined the songs and were asking me the words, the athmosphere that night was special. Many "tourists" do really add to it, rather than dilute it. But I get it, being "up for" a UCL home semi-final second leg is easy, and it gives nobody the right to criticise those who leave a bit early at home to Fulham on a wet Saturday afternoon.
If you normally leave early, maybe try stay a bit longer than normal, if you can't or won't, then no worries, try to make good use of the extra few minutes! Peace Brothers.