It's a good movie. It's not just a couple of catchy songs and good animation. It's funny, it has heart, satisfying character arcs, cool fight scenes and a decent, meaningful story. I don't think it does anything revolutionary, but it is competently made and has a wholesome message.
I think the issue for most is that it is clearly made for girls and we're still at a time where that means that it can't be considered good. I'm certainly not the first person to observe this irrational devaluation of all things girly (though there are always outliers that do specifically celebrate girly things), but since I got a little older and could let go of my own shame of enjoying some girly things, I have noticed that more and more. I suspect it's because "manly" stuff is celebrated so much. Even the trashiest, mid tier garbage "manly man" movies are somehow considered at least "ironically" cool and good, while girly movies have somehow to achieve way more to get the same amount of respect... anyway, rant over.
I think Kpop Demon Hunters is actually good and you will enjoy it if you like animated action-comedies and can enjoy movies that are targeted at girls (instead of boys).