Suika Game & Merge Puzzles
When two of the same fruit collide, they become one bigger fruit. That is the whole game, and by the end of 2023 it had spread across Japan through livestreams. Trace the lineage back and you find 2048 (2014), which merges numbers, and behind that, Tetris's act of stacking. As the myth note above explains, this format itself existed first in a Chinese browser game. Short, needing no explanation, fun to watch even when someone else is playing -- it had every condition that works in the age of livestreaming.
The myth, corrected
Suika Game was an original Japanese creation
Multiple sources point to its prototype as Merge Big Watermelon, a Chinese browser game that spread in January 2021. The format of merging matching fruit into bigger ones was already there; a Japanese company finished it as an app for projectors, and it exploded worldwide on Nintendo Switch at the end of 2023. No record of the creators acknowledging that influence could be found, so this map states only what could be confirmed: the format came from China, the explosion came from Japan.