I honestly find these genre breakdowns kind of misleading sometimes. A lot of readers just follow artists or series, not a label. But if you look at sales and what's getting new anime seasons, it's still the big three: shonen, shojo, and seinen.
Shonen stuff like 'Jujutsu Kaisen' and 'Chainsaw Man' is obviously massive—action, friendship, a bit of dark humor. But 'most popular' can mean different things. The romance and slice-of-life titles on apps like Manga Plus or the Shonen Jump app get insane daily read counts, things like 'Spy x Family' or 'Kaiju No. 8'. That's a different kind of popularity than buying physical volumes.
For me, the real interesting trend is how isekai, as a sub-genre, has absolutely saturated the space. It's its own beast now, but quality varies wildly from 'Mushoku Tensei' to a hundred cookie-cutter 'reborn in a game' stories. That's probably the most common thing you'll see, even if it's not always the most critically acclaimed.
The demographic labels still matter for marketing, but the lines are so blurry now. Plenty of adults read shonen, and plenty of guys read romance manga labeled as shojo. The genre tags are starting to feel more like content indicators than strict audience gates.