Only Up was a game on the likes of Getting Over It with Bennet Foddy, Pogostuck, or Jump King, meaning they were all games with the objective of getting to the top; while any misstep will send you down several hours of progress, the perfect game for streamers.
One of the significant issues with this game was not that the game wasn't entertaining; it was that the developer was found to be doing some questionable stuff, like using assets that did not belong to him or the presence of NFTs, which is always a sensitive subject, there wasn't any sign that the game was promoting them, they were just there, whether with that intention or not it is unclear.
The asset in question was one of an anime girl, which the creator of the model had stated that it was not made for commercial use, so using it in a $10 game (at the time) was not part of the plan; it was soon resolved in friendly terms with the original creator.
Now, the game's developer has decided that the game would be removed due to needing peace of mind and healing, which was definitely caused by all these controversies and probably other things.
There's no sign that the game will ever come back since the developer has decided to focus on their studies and shift focus to a future game, with the working title "Kith."