While version 1.6.640 was a positive update for casual players and Steam Deck users, it caused a disruption in the modding community.
: Once you have verified you are on 1.6.640, set your Steam settings to "Only update this game when I launch it" and always launch the game via SKSE to bypass the Steam launcher.
Released on September 20, 2022, this patch focused on several quality-of-life fixes for the Anniversary Edition content: Skyrim:Special Edition Patch - UESP Wiki