dxgi.dll
Skyrim Special Edition switched from 32 bit d3d9 to 64bit d3d11 as part of various engine improvements in this re-released version.
Also using any mod with the game (Regardless of what it is, just loading any .esm or .esp file.) will break achievement compatibility same as Fallout 4, to get around this there's a utility though as there's no script extender support just yet it's not as simple as just using that and a .dll file.
www.nexusmods.com/skyrimspecialedition/mods/245/
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(Loading a dxgi.dll injector or any other overlay for that matter shouldn't affect achievements though, odd.)