SteamOS 1 and 2 were Debian based, but SteamOS 3 (the version that launched with the Steam Deck) is Arch based.

My suspicion is that it is potentially a result of thinner shells. You look at something like Game Boy Color or Nintendo 64, and those things have quite thick shells with plenty of empty space inside, mitigating any potential structural loss due to transparency additives (ABS is not naturally transparent). Newer devices have thinner shells to reduce weight and maximize space for components, potentially leading to problems like this when using translucent plastic.

This is something of a reoccurring problem with translucent plastics.