Download the from the Nexus Mods website.
If you are convinced that 1.5.97 is for you, here is the canonical process (assuming you own Skyrim Special Edition on Steam, which auto-updates): skyrim ussep 1.5.97
The main issue for 1.5.97 users is that the official USSEP page on Nexus Mods only hosts the version compatible with the latest game update. Using a newer USSEP version on an older game version will cause immediate crashes at startup. Download the from the Nexus Mods website
Always launch your game via your mod manager using skse64_loader.exe , never through Steam. Step 2: Downgrade Your Game Always launch your game via your mod manager
To establish a stable 1.5.97 modding environment with the correct patch, follow these precise steps. Step 1: Downgrade Your Skyrim Executable
Stability in Stasis: An Analysis of the Unofficial Skyrim Special Edition Patch (USSEP) on Runtime Version 1.5.97