The adult tab has a game called Goodbye Eternity (that's its original name). I know this game, so I write Goodbye Eternity in the search bar. The letters are the same, but the page prompts that there is no such game.

I suggest a keyword search engine.

(AI translation)

The game does appear when searching for "Goodbye Eternity"

Being a game for adults, you must select the option that allows you to view that content and use a registered account, if not, by default itch hides all adult content and that is probably why you cannot see the game.

PS: An alternative is to search directly on Google indicating that you want it to search on the site: https://itch.io