I notice you're asking about — that version corresponds to Skyrim SE 1.5.97 , which was the last pre‑Anniversary Edition runtime (before the AE upgrade in November 2021).

: Modern versions of USSEP require the four free Creation Club mods (Fishing, Survival Mode, Rare Curios, and Saints & Seducers). If your 1.5.97 install lacks these, you must use the older 4.2.5b version. Installation Guide

To download the correct version of the Unofficial Skyrim Special Edition Patch (USSEP) for game version , you should look for version 4.2.5b