Practices that are not done today are not outdated either, they’re simply not being done
I am not sure if you use the word outdated correctly. Things that were done in the past and are not done now, are literally outdated. That's what it means. It also means old-fashioned. Antiquated. Or simply old. Depends a bit on context. Retro would fit the video game context probably best.
Also, ideas do can get outdated. There is nothing in the definition of the meaning of "idea" that prohibits this. So I am again not sure if you use this word correctly. Is this a case of lost in translation?
An idea is only timeless in the sense that you can claim the idea exists. But you need application of the idea. Like people believing the idea or acting on it. If this goes out of fashion, the idea is outdated. Even if some people still cling to the idea or try to revive it. Outdated things can become trendy again. Especially in fashion. Though I doubt we will see ruff collars any time soon. Or big game studios releasing a pure text game.