This file is part of vanilla Skyrim. It belongs to third-party mods or ENB/ReShade presets that modify frame rendering, anti-aliasing, or post-processing. The name suggests it’s related to maxing out frame buffers or ultra-frame rendering – often from:
maxsulframe.dll does not work in isolation. It relies on a specific version of the Skyrim Script Extender (SKSE64). skyrim maxsulframe.dll error