is there a way to get the whole gallery with some sort of cheat code? asking because I had already played through the whole content of the game, but I recently updated my hard drive and now I lost all the progress in the gallery, and I don't have a lot of free time to replay ALL of the game from the start

Unfortunately there is no cheat or any way to get CGs without playing scenes that are unlocking them

The restriction is intended to reward people that play through the game to access the CGs. In the past, we had people that would just rip through all the art assets and then ask when the next build was. So to prevent that and make it feel earned, we restrict how the CGs are unlocked by requiring them to have accessed the scenes.

Unfortunately in this case, you have already unlocked them by playing previously, but we don't have a work around, unless you go through the debug menu to access those specific scenes and play through them to unlock their CGs.