The game has no built-in option to invert the mouse Y-axis, and editing the
legacy Unity InputManager asset (e.g. via UABEA) has no effect — the
game reads mouse input through Unity's new Input System in its own code, not
through the legacy input axes. The only way to invert Y is to patch the
game's compiled code (Assembly-CSharp.dll) directly.
The game is built with the Mono scripting backend (not IL2CPP), which means
Assembly-CSharp.dll is a normal .NET assembly that can be decompiled,