I haven’t been part of the modding scene for a while now. But most likely, none of their public APIs were changed. Naturally, I could be wrong since I didn’t read the patch notes, but that’s typically not where it goes wrong.

Many modder, and I mean many, do not find Bethesda’s provided APIs to be sufficient for their goals. So people extend those APIs further with their own libraries and scripting engines. Then other modders build on top of that extensions. These work against the binary code of the game and contain a list of pointer addresses in binary. So even the smallest changes to the game binary ends up making all of these extensions to stop working.

These mods have a headache anytime any kind of updates are pushed. It’s an API thing, but it’s not the API Bethesda made.