Marvin
Frank
Dangelo
Boyz 2 Men
Sam Cooke
MJ would be in there but he’s more pop than R&B even tho he did R&B too
Would y'all count George Benson as an R&B artist? He definitely has albums that I would call R&B, but he often gets credited as a jazz artist and jazz guitarist, since that's what he started his career off doing and has many albums that are primarily just him playing guitar or playing covers of other songs before he began making more "traditional R&B" for his solo work. He's extremely slept on though.
Party
The Weeknd
Donell Jones
D’Angelo
Usher
HM: Jodeci, Chris Brown, Marvin, Al Green, Ginuwine, DVSN, and much much more