If you’re on the current game version, you need the latest USSEP (currently 4.3.3 or newer).
📢 PSA: The Essential USSEP File for Skyrim SE Version 1.5.97 (The "Golden" Version) unofficial skyrim special edition patch 1.5.97
The is the foundation of the "Classic" SE modding experience. It allows you to enjoy a bug-free Skyrim while retaining access to a decade's worth of advanced mods that haven't made the jump to the Anniversary Edition. If you’re on the current game version, you