By the end of 2021 and into early 2022, the 1.6.640 version became the new "standard" for those who wanted to use official Creation Club content alongside mods. Tools like the were invented, allowing players to run the new 1.6.640 content on the old 1.5.97 engine.
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If you are attempting to recreate a setup from this specific era (2021/early 2022) or trying to fix a broken install: skyrim+skse+16640+2021