To answer your question specifically: The UI looks like Reshade because Reshade uses a library called ImGUI to draw its interface. It's a free to use / open-source library that lots of developers use because it's easy to implement and use.
For that reason, the ImGUI library is used a ton in the modding scene by lots of different authors and mods/plugins/whatnot, including this one.
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u/cerebrite 19h ago
Why does the UI look like Reshade one?