This update for Skyrim Special Edition introduces Bethesda Game Studios Creations, an enhanced platform for building and sharing community-made content, as well as Steam Deck and ultrawide monitor support for PC players.
Tell it to only update on launch. If you then ONLY launch the game through the Script Extender, this doesn't count as a steam launch, and it shouldn't update. You don't necessarily need to be using any SKSE mods to launch that way, it just bypasses the normal launch process.
At least, that's the way it has always worked in the past. If you installed SKSE through Steam, YMMV; just get it direct from the dev website.
Edit: Just tried it out, and this mostly works. "Online Services" are disabled until you update, so any Bethesda.net mods installed inside the game itself may break, but mods installed from Nexus appear to be fine.
That is working for me (on linux) but the other thing you can do is make a backup of the game files before it updates and then restore the old version afterwards, according to this post on nexus
Damn unfortunate for me because this time around I didn't feel like using TES5Edit, Loot, and whatever other programs you needed to mod it properly and just did some light modding through the in game mod manager. Guess I'm just gona unplug my ethernet cable and launch it in offline mode for a few weeks.