Check their Velvet concept songs: Bad Boy, and definitely check the parent album Perfect Velvet. This is their r&b side, whereas their Red side is their more bonkers (and cutesy) one. Check also one of their earlier tracks, Automatic. Red Velvet have a really great discography, even if you don’t like their crazier title tracks, there’s always really good album tracks (Body Talk, You Better Know, Butterflies). Groups closer to Blackpink in sound and style could be CLC (single: No, mini album: No1); and GIDLE (check their singles Latata, Hann, Señorita); maybe try LOONA ODD EYE CIRCLE (mini album: Max & Match). Another cool group with more mature sound would be EXID.