The game was not delisted. If it were delisted, you would still see it in your collection.
It was removed from public access. Maybe deleted.
Some devs do this regularly.
https://itch.io/t/3693485/do-not-update-your-games-by-deleting-them-and-uploadin...
It also happens that games turn out to be malware. Or are removed by Itch for other reasons. But usually it was the dev that did it.
It is quite irritating either way. That we do not know which game, or why it is not available any longer.