To understand the significance of version 1.6.640, we must look at November 11, 2021.
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. skyrim+skse+16640+2021
: Right-click your SkyrimSE.exe in your Steam folder, select Properties > Details , and ensure the product version is 1.6.640.0 . To understand the significance of version 1