Yesterday the game was running fine on my Steam Deck. Today I accepted an update to 1.8.1.0.1871_1176.2658518_1871.2949264_28_0.2949264.5 and now, when I launch the game, gameplay is normal for about ten seconds, and then my frame rate starts to get worse and worse. After a few minutes it plateaus at what feels like about 10fps, which is much worse than normal.

(Strangely, after 3 launches producing this same result, I just tried a 4th time and my frame rate is normal, so I guess it's not 100% consistent...)