Their next handheld, the DS, was an experimental clamshell console with dual screens and a touch pad, yet was tasked with somehow recovering the ground lost to Sony while also being a worthy successor to the Game Boy name.
It was originally not meant as the "successor" to the game boy, but as a "third pillar" next to console and handheld gaming. This is because the 2 screens of which one was a touch screen was pretty niche at the time.
Soon they realized that its popularity and compatibility with classic handheld games made it a fine successor to game boy games, instead of a gimmicky console that only had a limited run.
They did launch the GB Micro after that, but it was just a very very small GBA SP so I guess that doesn't count.