This tool itself is redundant

[im-tem]

Vanilla Repentance reads its configuration from Documents/My Games/Binding of Isaac Repentance/options.ini. What's rather curious is that it has an option called "UseBorderlessFullscreen" which...allows the game to run in borderless window fullscreen. F.

[KMDEV99]

To clarify, I didn't find UseBorderlessFullscreen flag in options.ini, if You have the same issue just add it and set the value to 1. Works like a charm.