Skyrim has a thriving modding community that varies from improving graphics to adding alternate quest routes to designing new player homes. If you want something, odds are you can find it. But the new Anniversary Edition update will cause a lot of these mods to stop working.
For starters, SKSE won't be compatible which is the backbone for so many mods. You can't run SkyUI without SKSE and SkyUI is similarly used as the foundation for a lot of these addons. With both out of commission, a lot more will break.
Listed below are some of the most noteworthy mods that will stop working with the Anniversary Edition:
- TK Dodge
- Alternate Conversation Camera
- Better Jumping
- CBP Physics
- Classic Sprinting Redone
- Display Enemy Level
- Dynamic Potions
- Floating Damage
- Glow Be Gone
- Quick Loot
- RaceMenu
- True Directional Movement
- XP32 Maximum Skeleton
- moreHUD
- JContainers
- Named Quicksaves
- UIExtensions
You can find the full list here. It's extensive, but a lot of graphical mods should still work - hell, some standard Skyrim ones are compatible with the Legendary Edition. However, a lot of the more complicated, script-based ones won't. Most of Skyrim's later quality-of-life features stem from the community and so this is a big blow for players that are used to these enhancements.
But you can circumvent the update by launching Steam in offline mode. Doing so means that your modded playthrough will still work but you won't be able to try out the new Anniversary Edition until everything is brought up to speed. How long that takes is mostly dependant on the SKSE and SkyUI developers. For context, when the Legendary Edition first debuted, there was a long dry period. That's because the SKSE developers were busy. Modders aren't paid much if anything at all and it's not their day job. Nonetheless, certain mods found clever ways to work without SKSE, although they didn't tend to be as intuitive or clean.
Alternatively, as one user pointed out on Reddit, you can go to your "steamapps" folder and set "appmanifest_489830" to read-only. If Steam then tries to update Skyrim, it'll receive a disk write error. Whatever the case, you have a couple of weeks to prepare.