We do not create any requests or schemes in the RequestInterceptor. We just block them.
Please verify that in your build, MainWindow.cpp has LocalFileCanAccessFileUrls set to true here:
https://github.com/Sigil-Ebook/Sigil...ndow.cpp#L4292
Or perhaps try a clean checkout and build on Linux as new files were added so the CMakeLists.txt has changed.