The problems were caused by a Steam Deck client update released on April 1st, shortly after a general SteamOS update to version 3.6.24 the day before.

By design, the TDP slider on the Steam Deck will put a hard limit on how much power the CPU/GPU can draw from the battery. You can't get much more direct battery savings than that.

The Steam Deck OLED has a better screen, battery life, and Wi-Fi module. But power-wise, it’s identical to the original. Running a game on the Steam Deck OLED will be the same as on the Steam Deck.

On the other side, the Steam Deck OLED operates at a consistent TDP of 15W. You might think that the lower power would mean lower performance, but our tests showed something quite interesting.